No 10 Downing Street, once described by William Pitt the Younger as "my vast, awkward house", is the worst-designed place imaginable for running a country. The labyrinthine layout - a mixture of baroque state rooms, winding stairwells, secluded offices and poky passageways - actively hinders co-ordination between officials and advisers. The layout breeds petty rivalries: "like a medieval court", one long-serving mandarin says. The Prime Minister's orders are easily lost or deliberately misplaced. Britain is governed less from the corridors of power as from the broom cupboards of inertia.

Gordon Brown tried to solve the problem, exerting maximum control over the operation, by installing himself at the centre of a vast, open-plan "war room". David Cameron, less bothered by detail than his predecessor, reversed the innovation, returning the seat of prime ministerial power to more private quarters.

Cameron's intense relaxedness about the technicalities of government is, many Tories concede, his greatest weakness. Many of his political successes are really the accomplished disentanglement from troubles caused by earlier inattention. The "veto" he wielded at a European summit last year was pure escapology. Chained to the pro-European Liberal Democrats, submersed in the shark-infested waters of Tory backbench rebellion, the clock ticking, how would he get out alive? Then - ta-da! - he emerged as the man who finally said "no" to Europe, winning applause from his party and a boost in opinion polls. As political theatre, it was compelling but, as policy, the "veto" failed. The City was not protected from Brussels regulation; Britain's influence over the future reform of European trade rules was diminished.

Busking from the floor

Perhaps Cameron had no better option but that is because he neglected to put in the diplomatic work, building the alliances that would have given him more room for manoeuvre. He still has to go to Brussels and win arguments over things that he has prematurely sold to the country as victories.

Twice last year, during the phone-hacking scandal and after the inner-city riots, Cameron's grip of the situation came under serious question. Both times, he rescued himself with virtuoso busking from the floor of the House of Commons. The Tories are glad that their leader acquits himself well in a crisis but it bothers some of them that he needs exam conditions to perform.

That trait becomes especially problematic when combined with the natural tendency of Whitehall to bury or ignore difficult policy. Getting anything done requires a clear and consistent application of prime ministerial focus. Nor does it help that Cameron's director of strategy, Steve Hilton, has an even shorter attention span than his boss. Hilton is notorious for whimsical and sometimes outlandish policy fixations - he is fond of declaring that "nothing is off the table". He has a reputation for throwing tantrums when his ideas are blocked or ignored, as they often are. There are Cabinet Office officials who consider avoiding the implementation of Hiltonian diktats central to their job description.

Cameron is hardly the first prime minister to encounter this problem. In his second term in office, Tony Blair created a Downing Street "delivery unit" to overcome frustration at pulling on the "rubber levers" of Whitehall, which appear to yield but shift nothing on the ground. In opposition, Cameron and his inner circle devoured Blair's memoirs, paying particular attention to the former PM's regret at having squandered the early years of government, when he still had sufficient political capital to get difficult things done.

Having imbibed that lesson, the Tory leadership took a strategic decision to launch multiple policy "revolutions" across a number of fronts simultaneously. Cabinet ministers were given free rein to indulge their most ardent reforming urges. Some have fared better than others.

By far the most advanced is Michael Gove's education reform. (There is no more diligent a disciple of Blair in British politics than the Education Secretary.) Senior Labour figures privately accept that he has been highly effective in pushing his academies and free schools programme and that it is largely irreversible.

By contrast, Kenneth Clarke's liberal "rehabilitation revolution" in penal policy has been shelved on orders from Downing Street, for fear that it presented the government as "soft on crime". Iain Duncan Smith's universal credit, advertised as a miracle cure for welfare dependency, will emerge in October 2013 as a tweaked version of the existing benefits system, with a few perverse anti-work incentives taken out and some new ones added.

Off the rails

The biggest upheaval of all is taking place in the one public service that Cameron promised to leave unmolested. A vast NHS re-organisation, barely understood by the public, hated by doctors, will cause endless disruption with no compensating improvement in care. Health policy is, in the words of one Tory insider, "a train that has left the rails and is now sliding across the landscape". It can deliver only havoc.

What Cameron and Hilton once envisaged as a heroic, revolutionary tide looks more like a disjointed series of policy experiments. Some will be finished, some abandoned, some will work, others will blow up in the government's face. The end result certainly won't look like a coherent project to refashion the state and empower the "big society", no matter how many times the Prime Minister calls it that.

Since he became leader of the Conservative Party, Cameron has struggled to explain why it is that he wants to be in politics, other than because that is an agreeable pursuit for a man of his background and presentational skills. His greatest achievement has been persuading people that those qualities, combined with boundless self-confidence, are the natural markers of leadership and governing competence, making him the obvious candidate to clear up a mess left by the previous government. For his next trick, he must persuade people that he is also the right man to clear up the mess created by his own unfinished and neglected revolutions.