Tony Blair: Poster boy or cartoon villain?

Given that Blair's response to 9/11 led in a straight line to Britain's taking part in the invasion of Iraq 18 months later, and given that the Iraq war was the main reason Blair did not continue as Prime Minister for longer, solidarity with America – or, rather, solidarity with President Bush and meaning it – was a political error. Certainly, it is possible to see how a more cynical politician might have mitigated the anti-war rage by stepping back from military deployment in March 2003, an option explicitly offered by President Bush and described, but not, he says, advocated, by Jack Straw, the Foreign Secretary, on the eve of conflict.

It would have made little difference in Iraq, as the American forces would have gone in anyway, with the British presumably joining them afterwards, when the UN endorsed the international administration of the country in May 2003. But it would have made a difference in British politics, by separating British foreign policy from America's and avoiding the appearance of enthusiasm for bloodshed. It would also have avoided much of the bitterness of the accusation of deceit about the failure to find chemical and biological weapons after the invasion; and the descent of Iraq into disorder would have been seen differently if British troops had been deployed after the event to try to help stabilise the country.

A hint of this alternative history was given nine days before the invasion, on 11 March 2003. That was when Donald Rumsfeld, US Defense Secretary, said at a Pentagon news conference that Britain might not be able to take part in military action – he had just spoken to Geoff Hoon, his British opposite number, who had mentioned possible legal difficulties – but that "there are work-arounds".

Gordon Brown was thrown into 24 hours of panic and dismay. According to one witness, he was appalled at the prospect of Blair being hailed as a hero across anti-war Europe. He feared that Blair would use that popularity to resume his campaign to adopt the euro and to stay as Prime Minister after the date he had in mind for the handover, which was the middle of 2004.

However, stepping back on the eve of military action was not something that Blair wanted to do. There were probably only three people who could have prevented the UK from joining in the US-led invasion: Gordon Brown, Jack Straw and Peter Goldsmith. Brown, as an alternative prime minister, and Straw, as Foreign Secretary, could have rallied Labour MPs against military action; while Goldsmith, as Attorney General and thus the Government's legal adviser, could have made it impossible by advising that it was unlawful. Though Brown and Straw were less certain than Blair, they did not want Britain to stand aside either; but Goldsmith was another matter. His initial view was that UN resolution 1441, giving Saddam Hussein the "final opportunity" to comply with previous disarmament resolutions, was insufficient to provide a legal base for military action.

In February 2003, after discussing the history of the UN negotiations with US Administration lawyers, he had come round to the view that there was a "reasonable case" in international law for invasion, even without a further and more explicit UN resolution. But his advice was still hedged with warnings that the Government could be challenged in the courts. It was Hoon's concern about these warnings that had prompted Rumsfeld's public doubts about British participation. On that day, 11 March, Goldsmith told Blair "that he wished he could be much clearer in his advice, but in reality it was nuanced". Blair "knew", as Alastair Campbell recorded, "that if there was any nuance at all", Robin Cook and Clare Short "would be straight out saying the advice was that it was not legal, the Attorney General was casting doubt on the legal basis for war".

Goldsmith was persuaded, and told Straw that, "having decided to come down on one side" – that resolution 1441 was sufficient – he had also decided that in public he needed to explain his case "as strongly and unambiguously as possible". Blair told the Commons the next day, "I am determined to hold firm to the course that we have set out," and Brown went back to assuming that he would take over from him the following year.

With the legal obstacle removed, the decision facing the Commons on 18 March was whether it was in the national interest to join the US invasion. On this the most perceptive commentator was Cherie Blair, who said some years later: "A lot of the time these choices are not clear-cut. They are not black and white. Instead of being 80-20, many of them are actually more like 51-49. When taking those decisions, Tony is able to step back, absorb all the information and then choose. He is also very good at then convincing everybody else that it was a 70-30 decision all along. I think it was one of those 51-49 questions."

MPs decided, on balance, that the resort to military force was justified; the proportions in which they divided were 65-35. Half of Labour's backbenchers voted against. That vote broke the back of New Labour and was the end of Blair as Prime Minister. Extraordinarily, he fended off his departure, winning a third election in the meantime, for another four years.

He could have been Prime Minister for longer if he had been more sinuous. He could have opted out. Goldsmith gave him the excuse. Instead of saying, with steely politeness, that the Attorney General had to decide whether the action was lawful or not, and that "nuance" and "reasonable case" would not do, he could have said, "Oh well, it doesn't look as if we can do it, then." Brown's nightmare would have come true. Blair would have been hailed as the hero of the peace-loving Europeans who had tried but failed to restrain the lawless and reckless Americans. But that would have been out of character. He later said that he didn't think that Britain was that kind of country; what he meant was that he didn't think he was that kind of leader.

So it was a political mistake for Blair to have stood by Bush when he could have stood aside with honour; and the consequences of the invasion have been mostly negative. Yet his motive throughout, it seems to me, lay somewhere between the patriotic and the noble.

Blair survived as Prime Minister for so long because he managed Brown rather than confronted him. This in part reflected Blair's weakness, not of character but of the forces at his disposal. His consistent lean to the centre, which is what made him such a successful election winner, meant that his base of support in the Labour Party would always be shallow and conditional. Iraq broke that base. But Blair's survival was a reflection of Brown's weakness too. As Blair did with everyone – Paddy Ashdown, Roy Jenkins, Peter Mandelson, the Queen, even Alastair Campbell – he played Brown brilliantly, with as fine an understanding of psychology as anything in Jane Austen. If Brown had not been so psychologically flawed, he could have taken over in "late 2004", which is what Blair said in his memoir he had in mind the previous November, although that had been a moment of "the weakness of a normal person" who had been "ground down", or even "an act of cowardice".

But Brown was, unintentionally, Blair's best ally, and Blair sometimes failed to conceal his wonder that his rival was playing his hand so badly. If Brown had praised Blair, flattered Blair's Cabinet supporters and promised convincingly enough to carry on their programme, his succession would have been so much harder to resist. Campbell wrote that on 29 April 2003, "TB said surely Gordon must realise he is making it harder not easier to hand over to him. What is unfathomable is that it is such a not-clever strategy."

Thus Blair carried on for the equivalent of a full parliamentary term after the Iraq vote. His public service reforms, which hardly existed in 2001 and only now started to gather pace, were secured.

His main domestic monument were the improvements in education, the health service and cutting crime. The greatest acknowledgement of his achievement was the change in the Conservative Party. This is a true measure of a leader's historical significance. Just as the Tory party accommodated itself to Attlee's postwar settlement, and Blair himself marked Labour's accommodation to Thatcherism, by 2005 he had forced the Conservatives to put public services before tax cuts. Even in trying to close the deficit five years later David Cameron and George Osborne protected spending on the NHS and schools. The Conservative Party has abandoned the idea that people should be encouraged to opt out of the NHS; and who would have thought that the Tories would now be opposed in principle to extending selective state education?

What is just as important about David Cameron's liberal Conservatism is that it pays its respects to a Britain that is finally comfortable with equality for women and gay people. The legal breakthroughs for social liberalism came in the 1960s and 1970s, but the Conservative government, for 18 years in the 1980s and 1990s, was never reconciled to them. Under Blair, we got used to the idea of gay Cabinet ministers and a Parliament where people wear something other than dark suits.

When he finally took his leave of the Commons, on the day if not the year of his own choosing, Labour MPs, aghast at what they had lost, rose to give him a standing ovation. David Cameron, looking round, summoned his side of the House to join them in this breach of the convention against clapping. Paradoxically, the first time that convention had been broken was when Robin Cook's resignation speech in March 2003 prompted a partial standing ovation on the Labour side.

On balance, Blair was a good prime minister, outshone for partisans of left and right by Attlee and Thatcher respectively. He was unequalled in placing himself at the centre of gravity of the British electorate, and he delivered what was asked of him: the modest but lasting social-democratic reforms which were the best reflection of the ambiguous spirit in which he was elected in 1997.

Extracted from the Afterword, Tony Blair: Prime Minister, by John Rentoul, published as an e-book (£10.79) and paperback (£20) by Faber Finds this Thursday. IoS readers can buy the paperback at a special price of £16 when ordering at www.faber.co.uk/blair. To claim the offer please enter the promo code BLAIR at checkout. Offer ends on 16 July 2013. The book will be launched at 6.30pm on 2 July at the Mile End Group, Queen Mary, University of London, with a short talk, Q&A and drinks reception. Please email meg@qmul.ac.uk to attend.