Two months after the attacks of September 11, 2001, US Vice-President Dick Cheney and National Security Adviser Condoleezza Rice met George Tenet in the White House Situation Room. The presentation delivered by the director of the Central Intelligence Agency included unsettling information that, three weeks before September 11, two Pakistani nuclear scientists had met Osama bin Laden in Afghanistan. Characteristically, Cheney waited until the end of the briefing before giving his opinion: 'If there's a 1 per cent chance that Pakistani scientists are helping al-Qaeda build or develop a nuclear weapon, we have to treat it as a certainty. It's not about our analysis, or about finding a preponderance of evidence. It's about our response.'

This response-based approach to perceived threats - or the Cheney doctrine - came to define American policy towards al-Qaeda, as well as upending its traditional policy-forming process, writes Ron Suskind in The One Percent Doctrine.

Covering the period 2001-2004, and using Tenet's directorship as the framework for the book, Suskind traces the impact the doctrine had on both the US intelligence community and its targets. He elucidates this further by focusing much of his attention on the interplay of the CIA and senior Bush administration figures.

For suspected terrorists, this new creed would reveal itself in torture-by-proxy, whereby the US sent alleged al-Qaeda operatives from Afghanistan and elsewhere to countries such as Egypt, where brutal information-extracting techniques are a quotidian part of the secret police's repertoire.

For the CIA, Suskind says, the Cheney doctrine signalled an end to the critical and dispassionate analysis that had been its modus operandi. Its impartiality hijacked, the agency often found itself providing the Bush administration with intelligence that supported both its strategic goals and its daily political needs - to ensure, as Suskind writes, 'that America, for the most part, stayed on message'.

Perhaps the most public manifestation of this was Secretary of State Colin Powell's address to the United Nations on Iraq's weapons of mass destruction. With Tenet seated behind him, the CIA's imprimatur was stamped on the proceedings, even though many in the agency bridled at Tenet's appearance, given their serious misgivings about evidence of such weapons.

On the few occasions when the CIA wouldn't toe the line, the Bush administration sought the advice of a separate intelligence team in the Department of Defence, one whose findings usually could be counted on to endorse the suspicions of the vice-president and others. Such was the case when, in an attempt to link the September 11 attacks to Iraq, Cheney publicly argued that hijacker Mohamed Atta had met with Iraqi officials in Prague, and used Department of Defence intelligence to back him.

Still, the question remains why Tenet so forcefully described WMD in Iraq as a 'slam dunk'. Suskind suggests that by not having fired Tenet in the wake of September 11, President George W. Bush gained a grateful and unquestioning ally, a man so eager to erase the agency's public failings that he easily did the administration's bidding. Suskind gives equal attention to less enduring examples, including the capture of Abu Zubaydah. Held up by Bush as one of al-Qaeda's most important figures, Zubaydah turned out to be little more than a glorified travel agent for al-Qaeda operatives and their families. Yet the public was never told the truth, and 'knowledge of Zubaydah's limited role in al-Qaeda, and apparent insanity, was closely held and deeply classified'.

Even the most prejudiced of readers will find Suskind's latest work sobering. Given that nearly 2,600 Americans have now died in Iraq, proponents of that war may no longer be surprised to learn that Yusef al-Ayeri, the head of al-Qaeda on the Arabian peninsula, both predicted and hoped for a US invasion of Iraq. Worse yet, he formulated a 'strategy of remotely triggered explosives, suicide bombings, and lightning strike ambushes' to greet the invading force. So much for a response-driven strategy.

When The One Percent Doctrine stumbles, as it occasionally does, it's usually because Suskind's narrative non-fiction can seem clumsy or overwrought. Two- word sentences designed to add gravitas merely detract from an already profound tale. And in declaring that the London subway bombings of July 7 last year 'brought England to its knees', Suskind evidently hadn't passed through Heathrow just three days later, when the capital's airport seemed quite normal.

What Suskind has done, though, is to produce a book that will seduce anyone with an interest in the unseen war that the CIA and others have waged against America's enemies. More importantly, he has unveiled more of what the Bush administration kept from the public, not in the interest of national security, but because it suited.

As Howard Dean, the one-time Democratic presidential nominee, presciently remarked after the US government's raising of the terror threat status in 2004, 'It's just impossible to know how much of this is real and how much of this is politics.'