In this work of comparative political biography, former Labour MP Giles Radice portrays his subjects as a triumvirate of bright young men who "created New Labour, brought it to power and sustained it in government", dominating British politics for over a decade. Radice has the advantage of having known Tony Blair, Gordon Brown and Peter Mandelson for nearly 30 years, while keeping his distance intellectually. As a result, he gets far closer to the truth about New Labour than most biographers and political commentators have.

Radice is the author of two earlier comparative biographies - one dealing with his heroes Anthony Crosland, Roy Jenkins and Denis Healey, the other assessing the titans of the postwar government: Clement Attlee, Ernest Bevin, Herbert Morrison and Stafford Cripps. His argument is that the Blair and Brown governments, like Attlee's, have made Britain a fairer and more civilised society, bestowing a formidable social-democratic legacy.

Stepping back, nonetheless, one cannot help but conclude that New Labour wasted a historic opportunity. The glad, confident morning of May 1997 was the moment to reshape British politics and forge an enduring coalition for change. With advantages rarely enjoyed by its predecessors, New Labour ought to have become the natural party of government. But, as with Attlee, the opportunity was missed. The question remains why.

The answer to that depends on your world-view. Radice's account is one in which history is made by great men. A J P Taylor once remarked that "the history of modern Europe can be written in terms of three titans: Napoleon, Bismarck and Lenin". Had these men not lived, he argued, Europe's future would have taken a very different course in the 20th century. Like Taylor, the author is at risk of placing undue emphasis on the role of individual actors in shaping history.

In fact, the cult of leadership hero-worship at the heart of New Labour bred mutual suspicion and paranoia. It also brings to mind Machiavelli's remark in The Prince that "there is nothing more difficult to take in hand, more perilous to conduct, or more uncertain in its success, than to take the lead in the introduction of a new order of things", because the innovator has for enemies "all those who have done well under the old conditions, and lukewarm defenders in those who may do well under the new". Sensing enemies everywhere, New Labour achieved the distinction of uniting almost every shade of progressive opinion against it.

The Campbell diaries and Mandelson's Third Man only emphasise that there was a distinctly eccentric edge to their personal project. But New Labour was hardly the product of just three men's ingenuity and tenacity, however considerable the talents of the trio. This is a carefully cultivated myth that merits proper interrogation. In fact, too little attention has been paid to how all three men interacted with Neil Kinnock and John Smith in transforming Labour into a contender for power. There were also the early modernisers - Roy Hattersley, Bryan Gould, Mo Mowlam, latterly Robin Cook and, indeed, Radice himself - who believed that the party must become an agent of conscience and reform, and each of whom influenced Labour's rising stars. Then there were the MPs, the trade unionists and party activists who toiled throughout the 1980s and 1990s to make Labour into a potential party of government. History, including that of New Labour, is not made by great men alone.

Radice is surely right in his judgement that the party would have had a more substantial legacy had Blair, Brown and Mandelson combined effectively, rather than engaging in a fight to the political death. Yet to understand why the centre left squandered such a progressive moment, it is necessary to dig deeper. The answer lies in Labour's grappling with big structural challenges in British society, and not only the surface novelties of court politics.

Three central questions stand out. The first relates to globalisation and the fruitless search for a more just and efficient model of capitalism that would have strengthened the fundaments of the British economy prior to the financial crisis of 2008/2009. Second, there is the urgent need for thorough reform of our politics beyond piecemeal constitutional change, addressing the widening chasm between gov­ernment and citizen. Finally, there is the issue of Britain's search for a coherent place in the world after the demise of empire and the end of the cold war.

For all the strategic insight of New Labour as a response to the political hegemony of Thatcherism, it was the protagonists' failure to deal adequately with the economic and political challenges of the age that ultimately diminished their legacy. The three men's turbulent personal relationships and complex personalities make for fascinating reading, but ideas and institutions are what matter. It is these which remain, as ever, the forces of change.

Trio: Inside the Blair, Brown, Mandelson Project
Giles Radice
I B Tauris, 288pp, £20

Patrick Diamond is a former special adviser to the Labour government and a visiting fellow at Nuffield College, Oxford.