After 9/11 there was little that could shock former NYPD chief Bernard Kerik. He hadn’t reckoned, though, on post-war Baghdad, where he was posted to create a new Iraqi police force. What he initially imagined were the ravages of war and its aftermath turned out to be the quotidian consequences of three decades of totalitarian rule by a mafia family and the Ba’ath party.

Since the NYPD does not torture people, Kerik was shocked to discover torture chambers inside police stations. Abandoned videotapes recorded interrogations. Several films ended with a hand grenade being stuffed down the victims’ shirts, their bodies disintegrating with the pull of the pin; in one, Saddam himself appeared, impassively watching a suspect army general being devoured by Dobermans. Western human rights groups calculate that 300,000 Iraqis had been murdered since 1991, some fed feet-first into shredding machines, the majority just shot into mass graves. When Kerik began instructing recruits to the Iraqi police, he had to explain that “when you pull a man suspected of a crime into the station, you can’t hang him upside down and beat him with an iron bar”.

William Shawcross is one of a handful of European intellectuals who have bravely resisted the Gadarene rush to condemn Bush and Blair for liberating a country accurately described as “a prison above ground and a mass grave beneath it”.

Much of the international left’s hatred of Bush is explicable by a juvenile frustration at the replacement of a self-indulgent, vain baby-boomer who had been at Oxford by a focused, religious, Texan businessman who rejects everything they stand for. Some of this hatred has spilt onto Tony Blair, another decent man who is willing to use the word “evil”, and who in foreign policy has broken with the left’s habit of excusing squalid Stalinist or Third World dictators whenever they are opposed to America. The left used the term “resistance” to describe creatures who blew up Red Cross or UN relief missions.

Shawcross’s well-informed, lucid account of events leading up to (and beyond) the war explains why Bush and Blair were prepared to take such enormous risks, not just with their political careers, but with the lives of twentysomething farm boys from the Carolinas or motor mechanics from Middlesbrough. These risks include being committed to a war that is far from won; dividing and destabilising the UN, Nato and the EU; stirring up the Arab world; and pursuing a course that has been unpopular among bien pensants and wise-acres from Tariq Ali to Gerald Kaufman, those party turns of any “serious” British discussion.

The devastation visited on Manhattan by Saudi Arabian mass murderers raised the pressing prospect of Islamist terrorists acquiring, and using, more sophisticated weapons of mass destruction than hijacked passenger jets. Since Saddam had spent the better part of a decade trying to acquire such weapons, flouting endless attempts by the UN to dissuade him, and since he also funnelled funds to Palestinian suicide bombers, it seems not far-fetched to imagine that he might use the Al-Qaeda terrorist network to wage wars by proxy.

Nobody could guarantee that Al-Qaeda would not use Saddam’s arsenal of vials for its own nihilistic assaults against western civilisation since that organisation’s explicit aim is to kill millions of us. Any responsible leader has a duty to ensure that, no matter how remote the prospect, an avoidable catastrophe does not happen in the middle of Madrid, Rome or London. What will David Hare, Harold Pinter or Tariq Ali have to say, if and when a biological or chemical attack happens in London? That we had it coming to us?

Leadership was evinced, too, by Aznar, Berlusconi and John Howard, as well as by leaders of eastern European states to whom anti-Americanism is incomprehensible. Shawcross’s brilliant account of high-level diplomacy is unsparingly damning of the slippery Chirac and Schröder. The former has materially benefited his country, or perhaps just himself, by keeping Saddam in power. Having insisted that America work within a multilateral framework, France did everything to ensure that the process of consultation was fruitless. Both countries ruthlessly exploited anti-Americanism to gain electoral advantages, rallying the broad left while pandering to their large Muslim minorities, the subtext of much parliamentary Labour opposition to the war here.

The nation that gave the world Auschwitz also had the temerity to compare Bush with Hitler. True to form, the BBC, which every evening almost wills coalition failure in Iraq, invited the preeningly sinister Dominique de Villepin to deliver the Dimbleby Lecture about his country’s European “vision” — a vision whose reality will be a divided and impotent Europe snapping about the heels of an America whose leaders might decide that after 60 years Europe should pay for its own security, by closing hospitals, schools and universities.

Shawcross is not uncritical of the lack of foresight shown by an American leadership over-tantalised by “shock and awe” when it should have been thinking about sewers, water and policemen. But while Orla Guerin, the BBC’s in-house grim reaper, reminds us of coalition casualties, it is salutary to remember that much of Iraq resounds to pneumatic drills rather than machine guns, and that ordinary Iraqis are doing things we take for granted, such as reading a newspaper or using the internet, while not being subjected to Ba’athist surveillance.

The battle in Iraq is between the remnants of a regime based on mass murder, aided and abetted by Al-Qaeda pirates, and coalition forces who, in addition to maintaining security, are struggling to repair the infrastructure and to help shape civil society. To frustrate that mission, the powers of darkness have killed not just American soldiers, but such figures as Brazil’s Sergio Vieira de Mello who bravely decided to put themselves in such terrible danger. Let’s hope that Shawcross is right in believing that the coalition leaders have the will to stay that particular course. If they don’t, we will all bear the terrible consequences.

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