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Now you see it, now you don't: what optical illusions tell us about our brains

Illusions can offer insights into how the visual system processes images.

Maurits Escher: where do the staircases lead?

The human brain is a network of about 20 billion neurons – nerve cells – linked by several trillion connections. Not to mention glial cells, which scientists used to think were inactive scaffolding, but increasingly view as an essential part of how the brain works. Our brains give us movement, language, senses, memories, consciousness and personality. We know a lot more about the brain than we used to, but it still seems far too complicated for human understanding.

Fortunately, the brain contains many small networks of neurons that carry out some specific function: vision, hearing, movement. It makes sense to tackle these simple modules first. Moreover, we have good mathematical models of nerve cell behaviour. In 1952, Alan Hodgkin and Andrew Huxley wrote down the “Hodgkin-Huxley equations” for the transmission of a nerve impulse, which won them the 1963 Nobel Prize in Medicine. We also have effective techniques for understanding small networks’ components and how they are linked.

Many of these simple networks occur in the visual system. We used to think that the eye was like a camera, taking a “snapshot” of the outside world that was stored in the brain like a photo stuck in an album. It uses a lens to focus an image on to the retina at the back of the eye, which functions a bit like a roll of film – or, in today’s digital cameras, a charge-coupled device, storing an image pixel by pixel. But we now know that when the retina sends information to the brain’s visual cortex, the similarity to a camera ends.

Although we get a strong impression that what we are seeing is “out there” in front of us, what determines that perception resides inside our own heads. The brain decomposes images into simple pieces, works out what they are, “labels” them with that information, and reassembles them. When we see three sheep and two pigs in a field, we “know” which bits are sheep, which are pigs, and how many of each there are. If you try to program a computer to do that, you quickly realise how tricky the process is. Only very recently have computers been able to distinguish between faces, let alone sheep and pigs.

Probing the brain’s detailed activity is difficult. Rapid progress is being made, but it still takes a huge effort to get reliable information. But when science cannot observe something directly, it infers it, working indirectly. An effective way to infer how something functions is to see what it does when it goes wrong. It may be hard to understand a bridge while it stays up, but you can learn a lot about strength of materials when it collapses.

The visual system can “go wrong” in several interesting ways. Hallucinogenic drugs can change how neurons behave, producing dramatic images such as spinning spirals, which originate not in the eye, but in the brain. Some images even cause the brain to misinterpret what it’s seeing without outside help. We call them optical illusions.

One of the earliest was discovered in Renaissance Italy in the 16th century. Giambattista della Porta was the middle of three surviving sons of a wealthy merchant nobleman who became secretary to the Holy Roman emperor Charles V. The father was an intellectual, and Giambattista grew up in a house in Naples that hosted innumerable mathematicians, scientists, poets and musicians. He became an outstanding polymath, with publications on secret codes (including writing on the inside of eggshells), physiology, botany, agriculture, engineering, and much else. He wrote more than 20 plays.

Della Porta was particularly interested in the science of light. He made definitive improvements to the camera obscura, a device that projects an image of the outside world into a darkened room; he claimed to have invented the telescope before Galileo, and very likely did. His De refractione optices of 1593 contained the first report of a curious optical effect. He arranged two books so that one was visible to one eye only and the other to the other eye. Instead of seeing a combination of the two images, he perceived them alternately. He discovered that he could select either image at will by consciously switching his attention. This phenomenon is known today as binocular rivalry.

Two other distinct but related effects are impossible figures and visual illusions. In rivalry, each image appears unambiguous, but the eyes are shown conflicting images. In the other two phenomena, both eyes see the same image, but in one case it doesn’t make sense, and in the other it makes sense but is ambiguous.

Impossible figures at first sight seem to be entirely normal, but depict things that cannot exist – such as Roger Shepard’s 1990 drawing of an elephant in which everything above the knees makes sense, and everything below the knees makes sense, but the two regions do not fit together correctly. The Dutch artist Maurits Escher made frequent use of this kind of visual quirk.

In 1832, the Swiss crystallographer Louis Necker invented his “Necker cube” illusion, a skeletal cube that seems to switch its orientation repeatedly. An 1892 issue of the humorous German magazine Fliegende Blätter contains a picture with the caption “Which animals are most like each other?” and the answer “Rabbit and duck”. In a 1915 issue of the American magazine Puck, the cartoonist Ely William Hill published “My wife and my mother-in-law”, based on an 1888 German postcard. The image can be seen either as a young lady looking back over her shoulder, or as an elderly woman facing forwards. Several of Salvador Dalí’s paintings include illusions; especially Slave Market With the Apparition of the Invisible Bust of Voltaire, where a number of figures and everyday objects, carefully arranged, combine to give the impression of the French writer’s face.

Illusions offer insights into how the visual system processes images. The first few stages are fairly well understood. The top layer in the visual cortex detects edges of objects and the direction in which they are pointing. This information is passed to lower layers, which detect places where the direction suddenly changes, such as corners. Eventually some region in the cortex detects that you are looking at a human face and that it belongs to Aunt Matilda. Other parts of the brain are alerted, and you belatedly remember that tomorrow is her birthday and hurry off to buy a present.

These things don’t happen by magic. They have a very definite rationale, and that’s where the mathematics comes in. The top layer of the visual cortex contains innumerable tiny stacks of nerve cells. Each stack is like a pile of pancakes, and each pancake is a network of neurons that is sensitive to edges that point in one specific direction: one o’clock, two o’clock and so on.

For simplicity, call this network a cell; it does no harm to think of it as a single neuron. Roughly speaking, the cell at the top of the stack senses edges at the one o’clock position, the next one down corresponds to the two o’clock angle, and so on. If one cell receives a suitable input signal, it “fires”, telling all the other cells in its stack: “I’ve seen a boundary in the five o’clock direction.” However, another cell in the same stack might disagree, claiming the direction is at seven o’clock. How to resolve this conflict?

Neurons are linked by two kinds of connection, excitatory and inhibitory. If a neuron activates an excitatory connection, those at the other end of it are more likely to fire themselves. An inhibitory connection makes them less likely to fire. The cortex uses inhibitory connections to reach a definite decision. When a cell fires, it sends inhibitory signals to all of the other cells in its stack. These signals compete for attention. If the five o’clock signal is stronger than the seven o’clock one, for instance, the seven o’clock one gets shut down. The cells in effect “vote” on which direction they are detecting and the winner takes all.

Many neuroscientists think that something very similar is going on in visual illusions and rivalry. Think of the duck and rabbit with two possible interpretations. Hugh R Wilson, a neuroscientist at the Centre for Vision Research at York University, Toronto, proposed the simplest model, one stack with just two cells. Rodica Curtu, a mathematician at the University of Iowa, John Rinzel, a biomathematician then at the National Institutes of Health, and several other scientists have analysed this model in more detail. The basic idea is that one cell fires if the picture looks like a duck, the other if it resembles a rabbit. Because of the inhibitory connections, the winner should take all. Except that, in this illusion, it doesn’t quite work, because the two choices are equally plausible. That’s what makes it an illusion. So both cells want to fire. But they can’t, because of those inhibitory connections. Yet neither can they both remain quiescent, because the incoming signals encourage them to fire.

One possibility is that random signals coming from elsewhere in the brain might introduce a bias of perception, so that one cell still wins. However, the mathematical model predicts that, even without such bias, the signals in both cells should oscillate from active to inactive and back again, each becoming active when the other is not. It’s as if the network is dithering: the two cells take turns to fire and the network perceives the image as a duck, then as a rabbit, and keeps switching from one to the other. Which is what happens in reality.

Generalising from this observation, Wilson proposed a similar type of network that can model decision-making in the brain – which political party to support, for instance. But now the network consists of several stacks. Maybe one stack represents immigration policy, another unemployment, a third financial regulation, and so on. Each stack consists of cells that “recognise” a distinct policy feature. So the financial regulation stack has cells that recognise state regulation by law, self-regulation by the industry, or free-market economics.

The overall political stance of any given political party is a choice of one cell from each stack – one policy decision on each issue. Each prospective voter has his or her preferences, and these might not match those of any particular party. If these choices are used as inputs to the network, it will identify the party that most closely fits what the voter prefers. That decision can then be passed to other areas of the brain. Some voters may find themselves in a state akin to a visual illusion, vacillating between Labour and Liberal Democrat, or Conservative and Ukip.

This idea is speculative and it is not intended to be a literal description of how we decide whom to vote for. It is a schematic outline of something more complex, involving many regions of the brain. However, it provides a simple and flexible model for decision-making by a neural network, and in particular it shows that simple networks can do the job quite well. Martin Golubitsky of the Mathematical Biosciences Institute at Ohio State University and Casey O Diekman of the University of Michigan wondered whether Wilson’s networks could be used to model more complex examples of rivalry and illusions. Crucially, the resulting models allow specific predictions about experiments that have not yet been performed, making the whole idea scientifically testable.

The first success of this approach helped to explain an experiment that had already been carried out, with puzzling results. When the brain reassembles the separate bits of an image, it is said to “bind” these pieces. Rivalry provides evidence that binding occurs, by making it go wrong. In a rivalry experiment carried out in 2006 by S W Hong and S K Shevell, the subject’s left eye is shown a horizontal grid of grey and pink lines while the right eye sees a vertical grid of grey and green lines. Many subjects perceive an alternation between the images, just as della Porta did with his books. But some see two different images alternating: pink and green vertical lines, and pink and green horizontal lines – images shown to neither eye. This effect is called colour misbinding; it tells us that the reassembly process has matched colour to grid direction incorrectly. It is as if della Porta had ended up seeing another book altogether.

Golubitsky and Diekman studied the simplest Wilson network corresponding to this experiment. It has two stacks: one for colour, one for grid direction. Each stack has two cells. In the “colour” stack one cell detects pink and the other green; in the “orientation” stack one cell detects vertical and the other horizontal. As usual, there are inhibitory connections within each stack to ensure a winner-takes-all decision.

Following Wilson’s general scheme, they also added excitatory connections between cells in distinct stacks, representing the combinations of colour and direction that occur in the two “learned” images – those actually presented to the two eyes. Then they used recent mathematical techniques to list the patterns that arise in such a network. They found two types of oscillatory pattern. One corresponds to alternation between the two learned images. The other corresponds precisely to alternation between the two images seen in colour misbinding.

Colour misbinding is therefore a natural feature of the dynamics of Wilson networks. Although the network is “set up” to detect the two learned images, its structure produces an unexpected side effect: two images that were not learned. The rivalry experiment reveals hints of the brain’s hidden wiring. The same techniques apply to many other experiments, including some that have not yet been performed. They lead to very specific predictions, including more circumstances in which subjects will observe patterns that were not presented to either eye.

Similar models also apply to illusions. However, the excitatory connections cannot be determined by the images shown to the two eyes, because both eyes see the same image. One suggestion is that the connections may be determined by what your visual system already “knows” about real objects.

Take the celebrated moving illusion called “the spinning dancer”. Some observers see the solid silhouette of a dancer spinning anticlockwise, others clockwise. Sometimes, the direction of spin seems to switch suddenly.

We know that the top half of a spinning dancer can spin either clockwise or anticlockwise. Ditto for the bottom half. In principle, if the top half spins one way but the bottom half spins the other way, you would see the same silhouette, as if both were moving together. When people are shown “the spinning dancer”, no one sees the halves moving independently. If the top half spins clockwise, so does the bottom half.

Why do our brains do this? We can model that information using a series of stacks that correspond to different parts of the dancer’s body. The brain’s prior knowledge sets up a set of excitatory connections between all cells that sense clockwise motion, and another set of excitatory connections between all “anticlockwise” cells. We can also add inhibitory connections between the “clockwise” and the “anticlockwise” cells. These connections collectively tell the network that all parts of the object being perceived must spin in the same direction at any instant. Our brains don’t allow for a “half and half” interpretation.

When we analyse this network mathematically, it turns out that the cells switch repeatedly between a state in which all clockwise cells are firing but the anticlockwise ones are quiescent, and a state in which all anticlockwise cells are firing but the clockwise ones are quiescent. The upshot is that we perceive the whole figure of the dancer switching directions. Similar networks provide sensible models for many other illusions, including some in which there are three different inputs.

These models provide a common framework for both rivalry and illusion, and they unify many experiments, explain otherwise puzzling results and make new predictions that can be tested. They also tell us that in principle the brain can carry out some apparently complex tasks using simple networks. (What it does in practice is probably different in detail, but could well follow the same general lines.)

This could help make sense of a real brain, as new experiments improve our ability to observe its “wiring diagram”. It might not be as ambitious as trying to model the whole thing on a computer, but modesty can be a virtue. Since simple networks behave in strange and unexpected ways, what incomprehensible quirks might a complicated network have?

Perhaps Dalí, and Escher, and the spinning dancer can help us find out. 

Ian Stewart is Emeritus Professor of Mathematics and Digital Media Fellow at the University of Warwick

Charlie Forgham-Bailey for the New Statesman
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"I teach dirty tricks": the explosives expert who shows armies how to deal with terrorists

Sidney Alford used to blow things up in his garage. Now his expertise is helping save lives.

“I’ll fetch the hammer,” says Sidney Alford, leaving me in a laboratory filled with mysteriously named drawers and small bottles with skulls on their labels. When he has fetched it – “it’s a jeweller’s hammer, given to me in Paris by a friend of Salvador Dali” – the 82-year-old plans to tap gently on a small mound of white powder called triacetone triperoxide, or TATP, better known as the explosive favoured by Isis in their suicide belts and homemade bombs. Because of its instability and destructive power, its nickname is “Mother of Satan”.

Tapping it with a hammer is enough to make it go bang.

Directing me to stand by the door, he searches for ear plugs before stuffing some paper in his ears – “I’m quite deaf, you know,” were almost his first words to me that morning – and begins to tap the Mother of Satan. On the fourth tap, it explodes in a genteel fashion with a flash and a pop. Its sensitivity to percussion is one of the reasons that jihadi bomb-makers suffer so many workplace accidents. “See,” Alford says. “You’d be OK walking, just don’t fall over or get shot.”

I have wanted to meet Sidney Alford ever since I heard about him from the investigative journalist Meirion Jones, who once uncovered a British man who sold £50m-worth of fake bomb detectors in Iraq and other countries. (The fraudster, James McCormick, was jailed for ten years in 2013.)

Giving a presentation to students, Jones mentioned that he could prove the gadgets were useless – just black boxes with radio aerials sticking out of them – because he had taken them “to a guy the BBC uses for explosives, who has a quarry in Somerset where he blows things up”. I decided then and there that I was very interested in being in a quarry in Somerset where someone blew things up. Maybe I would even get to press the button.

There was a less childish reason for visiting, too. Sidney Alford’s life story is interwoven with one of the technologies that defines the modern world: explosives. We fear explosives – suicide bombs, car bombs, bombs on aircraft – but we also need them, for everything from realistic film scenes to demolition. (Alford has a letter from Stanley Kubrick thanking him for his help on Full Metal Jacket.) Surprisingly, the best way to defuse an explosive is often with another explosive, something that Sidney’s company, Alford Technologies, has pioneered.

In other words, if you want to make something go bang – or, just as importantly, stop something going bang – he is the man to talk to. Quite loudly.

***

The first explosive materials Alford ever saw were fragments of bombs and V2 rockets left over from the German shelling of London. Born in 1935 in the suburb of Ilford, he moved with his family to Bournemouth when the Second World War broke out. When he returned, he found rich pickings in his battered neighbourhood in the form of magnesium incendiary bombs, which he filed down and turned into fireworks.

I ask him if, like my own father, he ever frightened his teachers with nitrogen triiodide, an unstable explosive compound that schoolchildren used to make themselves and set off in lessons to terrify unwary members of staff in the era before health and safety. “Oh yes,” he says. “I put it under my French teacher’s chair.” A pause. “He’d been in the army, so he didn’t make a fuss.”

Alford went to a grammar school, where he was an undistinguished pupil, angry that the headmaster wouldn’t let him learn German (rather than Latin) so he could speak to the Jewish child refugees he knew. But he was always interested in chemistry, and “by the fifth form, I’d recruit classmates to make bigger bangs”.

A chemistry degree came next, followed by a series of odd jobs, including diet research and studying the brain, an MSc in the science of environmental pollution, and two business associations with men he now characterises as “bad sorts”, who ripped him off.

By this time, he had moved to Ham, in west London, and had begun to take his chemistry experiments more seriously. It was the early 1970s, and the IRA’s bombing campaign had come to England. How could these weapons be neutralised, Alford wondered? Was it better to encase suspect packages in “blast containers”, or use shaped charges – typically, small cones that focus explosive energy into a point – to disrupt their ability to go off?

A brief digression on explosives is necessary here. When you think of something going bang in a spectacular fashion, that’s a detonation. “Detonare,” says Alford at one point during my tour of the quarry, relishing the Latin. “Like thunder.”

High explosives such as TNT, nitroglycerin or Semtex can be detonated by administering a violent shock to the main charge using a small amount of relatively sensitive and violent material in a metal capsule. This creates a hot shock wave, which sweeps through the substance faster than the speed of sound.

Old-fashioned gunpowder, house fires and your car’s internal combustion engine go through a different process, known as “deflagration”, where the chemical reaction moves through the molecules much more slowly. This burning is usually less dramatic and easier to manage. (Alford hates the term “controlled explosion”, reasoning that an expert should always control their explosions. If they fail, it’s a cock-up.)

The theory goes, then, that if you attack a munition just hard enough to ignite its contents but without causing a violent shock wave, it will deflagrate but, on a good day, it will not detonate. “Yes, it might make a massive fireball, but I’ve done it in jungles under a tree,” says Alford. “[With deflagration] the tree may lose most of its leaves, but with detonation, there is no tree.”

In the 1970s, he set up a makeshift laboratory in his suburban garage. There, he would experiment with making explosive charges, using measured quantities of material in different casings. He would leave his car engine running so any bangs could be plausibly written off as backfiring.

This cover story clearly didn’t wash with the neighbours, though, as first the police and then MI5 – “the most gentlemanly man” – came round to see why exactly a chemistry graduate they had never heard of was blowing stuff up in his suburban garage. When he explained himself to the security services, they put him in touch with the Ministry of Defence, and he was offered a contract.

***

Alford Technologies has a slogan: “For when you can’t afford to fail”. It also has an office in a business park outside Trowbridge in Wiltshire, but the real action happens at its testing ground, a former quarry amid the rolling hills of the Mendips, not far outside Bath. It feels like a cross between a scrapyard and a building site. “Here’s the bottom half of a Soviet mine, which we use as a brazier,” says Alford at one point, prodding it with a toecap.

Soldiers from various armies come here to learn about explosives and how to render them harmless. It’s vital work: last year in Iraq and Syria there were dozens of car bombs, with a single one in Baghdad claiming 250 lives. In Manchester this year an Isis-inspired jihadi killed 22 concert-goers and injured 250 with a backpack bomb apparently built from instructions found
on the internet.

Learning to counter such threats means understanding them; jihadists and other terrorists might have access only to basic materials, but many also display great ingenuity. When I ask why Alford has a packet of Tampax in his lab, he says the tampons can be dipped in liquid explosives and turned into cartridges: “I teach dirty tricks so they don’t get caught out by them.”

Sidney Alford’s contributions to the world of explosives rest on an unlikely substance: water. When he first began tinkering in his garage in the 1970s, engineers had already worked out a rough-and-ready way of disabling improvised explosive devices (IEDs). They used a gun barrel loaded with a blank cartridge to fire a jet of water that broke through the explosive’s casing and disrupted it. However, a sufficiently strong casing – say, one made of steel – could defeat this method.

In a low outbuilding in the quarry, Alford shows me his answer to this problem. Within a shaped charge, the force of a small explosion collapses a metal cone, turning it inside out and extruding it into a long, thin rod that shoots out at high velocity, about five times faster than a bullet.

The young chemist had an idea: why not combine the water from the older gun-barrel method with the accuracy and force of the metal jet in a shaped charge? In Alford inventions such as the Vulcan and the Pluton, the explosive charge shoots a targeted jet of water at high speed and with incredible accuracy.

Ho ho, you’re thinking. Water! Very scary. This is broadly what I thought until I saw one of Alford’s smaller shaped charges in action. After the demonstration with the hammer, he put on a pair of sturdy boots instead of brogues and we hopped into a small four-by-four to get to the base of the quarry. “Should I take my safety glasses?” I asked, even though we would be inside an old reinforced lookout hut salvaged from the Maze prison in Northern Ireland. “Oh no,” replied Alford. “If it goes wrong, it will kill you. No need to waste a perfectly good pair of glasses.”

The Vulcan is about six-inches long, with a case of grey plastic, and loaded with 30g of plastic explosives with a cone of water held in front of it. The explosive is “about two toasts’ worth of butter,” said Alford’s project manager, Matt Eades, who served in the Royal Engineers for 25 years.

Alford placed the charge above a 10mm-thick steel plate using the aluminium-wire legs as a tripod, inserted an electric detonator into the Vulcan, and we retired to the hut, whose thick, double-glazed windows gave a good, if smeary, view of the sandpit. “If you write a nice, ingratiating article about me you can press the button,” said Alford.

I pressed the button.

There was a significant bang, making me glad of my ear defenders, but the plume went straight upwards. When we ventured out to the sandpit, Alford practically skipped up the side and fished out the metal plate, now with a clean-edged circular hole punched straight through it.

This practical demonstration had followed a whirlwind tour of the various Alford Technologies products and a brisk explanation of the theory of explosives. Alford clearly enjoys naming his creations: the Vulcan sits in his display alongside the Krakatoa and the Vesuvius, which can also be used for bomb disposal and demolition. The BootBanger is so called because “it bangs car boots” while the Van Trepan cuts a neat, round hole in the top of a larger vehicle. The Bottler is not only shaped like a bottle, but named for the Australian slang “that’s a bottler”, which Alford translates as “the cat’s whiskers”.

Even the Dioplex, a linear charge that creates a chopping blade, has a story attached: “I thought it was a do-it-yourself device, but I thought ‘do it oneself’ sounded better. So: ‘Do It Oneself Plastic Explosive’.”

One of the things a trip to the quarry teaches me is that the ways in which humans try to kill and maim each other are nothing if not inventive. The company sells a version of a Bangalore torpedo, an old invention used by Alford’s own father when he fought in the First World War. This is a modular tube you can push underneath barbed wire, blowing it apart to clear a path for infantry. A stronger version was needed, Alford says, because of the advent of razor wire. “Barbed wire was soft steel, designed to keep in cows. Razor wire was designed to cut you.” The new Alford Bangalore Blade torpedoes through the wire coils, severing them using four aluminium cutters and creating an unobstructed 10m route through.

The Breacher’s Boot is a door-shaped panel filled with water, used to punch through walls in hostage situations. “It gives a ‘kick’ to the wall, so bits of it will fall down. You don’t want to use shaped charges then,” he says. “If there’s a person on the other side of the wall, you’d cut them in half. And if you simply used a mass of high explosive, the concrete would fly almost horizontally.”

A similar idea lies behind the Alford Strip, a sticky rope of explosives and tamping material used in terror arrests, where the police would once have used a sledgehammer to open a door, but are now much more worried about booby traps. You run the 25mm- or 42mm-long plastic extrusion down a door, window or wall and then lay a length of det cord far enough away from it to put service personnel at a safer distance.

Down in the quarry, having punched through one square steel plate, we now try ten taped together versus a 40g load of explosives and a copper cone. The result: a 2m-high flash and the same clean hole – although the jet doesn’t make it through all ten plates. It stops at seven.

This isn’t an error: the shaped charges can use copper, water, aluminium or magnesium, depending on the force and space needed. Magnesium is incendiary; water and aluminium might be chosen because they lose velocity very quickly. You cut through what you want to cut through, without damaging either the structural integrity of the object surrounding it or innocent bystanders.

This precision is particularly important in demolition work. Last year, Alford Technologies took over the contract to break up Didcot Power Station, slicing through steel beams to dismantle the decommissioned building. It was called in after a terrible accident on 23 February 2016, when four workers employed by a respected firm, Coleman and Company, were killed while trying to lay charges inside the structure. “There was this crash – I looked over my shoulder and saw the boiler coming down,” one of the survivors, Mathew Mowat, told the Birmingham Mail. “We ran in self-preservation – then there was a loud bang and a massive cloud of dust, we couldn’t see much for a few minutes.”

It took months to recover the bodies of all four missing men, who had to be identified from dental records and tattoos.

***

Over an Eccles cake in the main office, Alford tells me about some of his other jobs, including cutting up sunken ships in the Persian Gulf during the “Tanker War” of the mid-1980s, between Iran and Iraq, and joining a mission to retrieve £40m in gold bars from HMS Edinburgh, which sank in 1942 off the coast of Norway. (It was carrying 4,570kg of Russian bullion destined for the western allies.) The ship had been designated a war grave to stop it being plundered, and an air of mystery hung over the whole salvage project. Alford was told not to mention that he was an explosives expert.

Perhaps unsurprisingly, his work – and his anti-authoritarian streak – has caused conflict. “I’m doing things government departments ought to be doing,” he tells me in the car on the way to the quarry. “I’m in the anomalous position of someone who is quite admired, but also quite despised. Civil servants hate my guts.” When he was 40, he says, he asked for a formal job working with the department of defence, “and was told I was too old to have new ideas”. He set up Alford Technologies in 1985, and it now employs six people. The latest set of accounts at Companies House value the firm’s net worth at £2.3m.

Although Alford is scrupulously careful when handling explosives, he loathes health-and-safety culture. As we tramp round the quarry, he indicates a sign next to a pond, reading “Deep Water”, and tuts theatrically. He voted for Brexit to give the establishment a kick, not thinking it would actually happen.

It is a source of great chagrin that the government breathes down his neck, regulating what compounds he can keep and how he can keep them. “You have to have a licence for every substance,” he tells me in the car. “I’ve got them all. Well, it might be different if I wanted to go nuclear.”

 In 1996, he decided to make a stand against the pettifogging bureaucracy that, as he saw it, interfered with his work. Spooked by the thought of Irish republican terrorism, the regulators had insisted that he had to put a lock on his explosives store. “I told them that if the IRA really wanted to get my explosives, they would kidnap one of my family.” (He has two sons with his Japanese-born wife, Itsuko; the elder, 46-year-old Roland, now runs the business.) Besides which, he didn’t see why he should put an alarm on his few kilos of various explosives when the farmer next door had tonnes of ammonium nitrate fertiliser, a key ingredient in the IRA’s bomb-making.

The stand-off broke when his request to renew his explosives licence was turned down; soon after, the police came to raid his stores. He had tipped off a friendly journalist, however, and the visit was captured on camera and written up first in the local paper and then the Daily Mail, where Christopher Booker took up the cause of a Englishman’s inalienable right to keep high explosives in his shed. “I felt morally obliged to be prosecuted,” he says now.

The court case, documented in the newspaper clippings, sounds like a mixture of deadening legal procedure and high farce. At the magistrates’ court, Alford and a friend pursued and rearrested the next defendant, who tried to do a runner; when his case was kicked upwards to Swindon Crown Court, he turned up in an armoured Daimler Ferret, posing for photographs with his head poking out of the top, white hair tucked into a helmet. He was eventually charged with possessing explosives without a licence and fined £750, with £250 costs. The judge ordered the police to give him his licence back, but ticked him off for using the court system for political purposes.

Listening to this story, it becomes clearer why Alford never ended up in the warm embrace of an official government role. He offered his ideas to the Ministry of Defence, but he shows me a letter from April 1977, where an unlucky official reveals that he is “regarding your correspondence with diminishing enthusiasm”. Still, he is sanguine. “Most of my enemies have now gone to the laboratory in the sky, or retired,” he says. “I’m glad I didn’t work for them. Would I have fitted in? Probably not.” In any case, he has had some official recognition, receiving an OBE in 2015.

***

Alford’s work is used in war zones including Afghanistan, but also places like Cambodia, which are still riddled with unexploded ordnance from previous ground wars. Over the years, he has visited that country and Laos several times to practise new ways of dealing with old bombs. (The company produces a more affordable version of the Vulcan for non-military use.) He first went to Vietnam during the war; the last person, he says, to get a Japanese tourist visa into the country in the 1950s. The company’s brochures show smiling locals posing next to the sleeping monsters they have had to live alongside for decades.

But Iraq, too, is in dire need of methods to deal with cheap, homemade explosives. After Matt the Ex-Army Guy and Alford have demonstrated how to blow a door off its hinges, cut through a 50mm steel bar, and turn a fire extinguisher inside out – “that is unzipped in all known directions, it is a former IED,” says Alford, Pythonesquely – they show me the Bottler and the BootBanger.

They drag beer kegs into the boot of an old blue Nissan Almera, explaining that these were a favoured IRA device: who questions a few beer kegs in the street? First, they stick a Bottler between the front seats, showing how you would disrupt any electronics without setting the vehicle on fire – which would destroy forensic evidence. “They’d usually use a robot,” explains Matt. “And the robot usually leaves [the area], because they’re expensive.” A six-wheeler bomb disposal robot costs around £750,000.

We retreat again to the hut. I must be looking increasingly nervous, because Alford tries to reassure me about the building’s structural integrity: “If it tips over, it will take two weeks to get you out. But they’ll know where to find your body.”

As promised, the explosion is focused – and controlled, in the Alford-approved sense of the word. The windscreen is peeled back, lying on the roof, but the fuel tank didn’t ignite and the back windows are intact. “I know it might look like a mess,” says Matt, “but this would be classified as a result. You use a smaller bit of explosive to get rid of a larger one.”

Finally, it’s time for the big one. Matt slides the BootBanger, shaped like a suitcase, under the back end of the car. It has a curved sheet of 400g of plastic explosive through the middle, sandwiched by water on both sides and encased in nondescript grey plastic.

Now this is a bigger bang. I suddenly see the point of all those “Blasting!” warning signs that surround the quarry. If you drove past and heard this, you’d think the Russians had invaded. As an orange-red flame flashes and a deep, throaty boom fills the quarry, the beer kegs are fired out of the back of the car, pinwheeling 20 feet in the air and coming to rest yards away. Debris rains down on the roof of the hut. I swear I can hear the plinking sound of metal cooling. The car is now missing its back windscreen, and is, it’s fair to say, probably never going to pass another MOT. Nevertheless, it is still recognisably car-shaped; the skeleton is undisturbed.

Unfazed, Alford hurries to the car, and plucks a piece of paper from the boot, clearly left there by a previous owner. It is undamaged.

And then it’s time to rejoin the real world. As he drives me back to Bath, I ask Alford what it feels like to do what he does. He has saved possibly hundreds, maybe thousands of lives. “Yes, but in an already over-populated world,” he sighs.

I know he doesn’t mean it callously; he just doesn’t want credit for what, in his eyes, is barely a job at all. The schoolboy who wanted to make a bigger bang got his wish. 

Helen Lewis is deputy editor of the New Statesman. She has presented BBC Radio 4’s Week in Westminster and is a regular panellist on BBC1’s Sunday Politics.