By Tom Bower
Faber & Faber, £20

Oscar Wilde once said that every great man has his disciples, but it is always the Judas who writes the biography. Tom Bower, an investigative journalist, was never a disciple of Blair's, though he voted for him in 1997 and supported the Iraq war. He is now thoroughly disillusioned. And Broken Vows is a hatchet job.

Bower focuses on five areas where he believes that Blair failed - health, education, immigration, energy and the wars in Afghanistan and Iraq. He discusses only in passing the major constitutional reforms that Blair implemented - the Human Rights Act, the London mayoralty, devolution, and the Belfast Agreement, which brought peace to Northern Ireland. These reforms have made Britain a better governed country than it was when Blair took office in 1997.

Broken Vows is based largely on interviews with retired civil servants, who seem to have spoken with remarkable candour. The book reports verbatim detailed conversations held many years ago with suspicious exactitude. It is difficult to believe that memories are so accurate and untinged by hindsight.

It is perhaps not surprising that Blair's informal methods of "sofa government" were not to the taste of officials. Previous Labour Prime Ministers had been criticised for succumbing to the Whitehall establishment. Blair is criticised for resisting it.

It is, Bower believes, largely because Blair ignored official advice that he decided on war with Iraq. It turned out that Saddam Hussein did not have weapons of mass destruction, though most intelligence services - not just the British and American - believed that he did. But, had Britain and America not gone to war, Saddam would probably have sought to acquire them. Had Iraq, as a nuclear power, then invaded Kuwait or Saudi Arabia, the world would have asked why Britain and the US did not remove Saddam while they had the chance. Had Britain and France removed Hitler in 1936 when he broke the Treaty of Locarno by reoccupying and remilitarising the Rhineland, there would no doubt have been vociferous protests from the stage army of the good.

We all know the consequences of the war. We can never know the consequences of not going to war.

It was Blair's support for Israel in its war with Lebanon in 2006 that pushed Labour MPs into insisting that he announce a date for his departure. The criticism by Labour MPs of "Israeli excesses" was, Bower says, "echoed by a commission chaired by an Israeli judge appointed by the Israeli government".

In fact, the Winograd Commission did not discuss "excesses" but, rather, failings in Israel's political and military decision-making machinery, and it deplored the fact that Israel had not secured a clear, military victory.

But Hizbollah leader, Hassan Nasrallah, said that he would not have kidnapped two Israeli soldiers had he known that it would lead to war; and, since 2006, there has been relative peace on Israel's northern border.

Broken Vows makes no pretence to be a balanced biography. It is the case for the prosecution, told with verve but at excessive length. It fits the mood of the times, including within the Labour Party, which seems never to have forgiven Blair for winning three elections and has turned him into a pariah. But there is much more to be said for the Blair governments than Bower is prepared to acknowledge.

Vernon Bogdanor is Professor of Government at King's College, London