In 1992, Mark Higson, the Foreign Office official responsible for Iraq, appeared before the Scott inquiry into the scandal of arms sold illegally to Saddam Hussein. He described a "culture of lying" at the heart of British foreign policymaking. I asked him how frequently ministers and officials lied to parliament.

"It's systemic," he said. "The draft letters I wrote for various ministers were saying that nothing had changed, the embargo on the sale of arms to Iraq was the same."

"Was that true?" I asked.

"No, it wasn't true."

"And your superiors knew it wasn't true?"

"Yes."

"So how much truth did the public get?"

"The public got as much truth as we could squeeze out, given that we told downright lies."

From British involvement with the genocidal Khmer Rouge in Cambodia, to the supply of warplanes to the Indonesian dictator Suharto, knowing he was bombing civilians in East Timor, to the denial of vaccines and other humanitarian aid to the children of Iraq, my experience with the Foreign Office is that Higson was right and remains right.

As I write this, the dispossessed people of the Chagos Islands in the Indian Ocean await the decision of the Law Lords, hoping for a repetition of four previous judgments that their brutal expulsion to make way for a US military base was "outrageous", "illegal" and "repugnant". That they must endure yet another appeal is thanks to the Foreign Office - whose legal adviser in 1968, one Anthony Ivall Aust (pronounced "oarst" and since knighted), wrote a secret document headed "Maintaining the fiction". This advised the then Labour government to "argue" the "fiction" that the Chagossians were "only a floating population". Today, the depopulated main island, Diego Garcia, over which the Union Jack flies, serves the "war on terror" as an American interrogation and torture centre.

Obama’s job is to present a benign, even progressive face that will revive America’s democratic pretensions, while ensuring that nothing changes

When you bear this in mind, the US presidential race becomes surreal. The beatification of President Barack Obama is already under way; for it is he who "challenges America to rise up [and] summon 'the better angels of our nature'", says Rolling Stone magazine, reminiscent of the mating calls of Guardian writers to the "mystical" Blair. As ever, the Orwell Inversion Test is necessary. Obama claims that his vast campaign wealth comes from small individual donors, yet he has also received funds from some of the most notorious looters on Wall Street. Moreover, the "dove" and "candidate of change" has voted repeatedly to fund George W Bush's rapacious wars, and now demands more war in Afghanistan while he threatens to bomb Pakistan.

Dismissing the popular democracies in Latin America as a "vacuum" to be filled by the United States, he has endorsed Colombia's "right to strike terrorists who seek safe havens across its borders". Translated, this means the "right" of the criminal regime in that country to invade its neighbours, notably uppity Venezuela, on Washington's behalf. The British human rights group Justice for Colombia has just published a study concerning Anglo-American backing for the Colombian regime of Álvaro Uribe, which is responsible for more than 90 per cent of all cases of torture. The principal torturers, the "security forces", are trained by the Americans and the British. The Foreign Office replies that it is "improving the human rights record of the military and combating drug trafficking". The study finds not a shred of evidence to support this. Colombian officers with barbaric records, such as those implicated in the murder of a trade union leader, are welcomed to Britain for "seminars".

As in many parts of the world, the British role is that of subcontractor to Washington. The bloody "Plan Colombia" was the design of Bill Clinton, the last Democratic president and inspiration for Blair's and Brown's new Labour. Clinton's administration was at least as violent as Bush's - see Unicef's report that 500,000 Iraqi children died as a result of the Anglo-American blockade in the 1990s.

The lesson learned is that no presidential candidate, least of all a Democrat awash with money from America's "banksters", as Franklin Roosevelt called them, can or will challenge a militarised system that controls and rewards him. Obama's job is to present a benign, even progressive face that will revive America's democratic pretensions, internationally and domestically, while ensuring nothing of substance changes.

Among ordinary Americans desperate for a secure life, his skin colour may help him regain this unjustified "trust", even though it is of a similar hue to that of Colin Powell, who lied to the United Nations for Bush and now endorses Obama. As for the rest of us, is it not time we opened our eyes and exercised our right not to be lied to, yet again?

"Heroes: the Films of John Pilger (1970-2007)" is released on DVD on 27 October

www.johnpilger.com