Secret scorers in the Premier league

What's gone wrong at No 10? Could it be the rise of the unaccountable 'adviser'

Churchill called them "weathermakers" - the rare politicians who, to repeat Peter Hennessy's mixed metaphor, "set the terms of political trade". In his monumental study, Hennessy examines the claims of Clement Attlee and Margaret Thatcher to membership of that exalted band.

Churchill called them "weathermakers" - the rare politicians who, to repeat Peter Hennessy's mixed metaphor, "set the terms of political trade". In his monumental study, Hennessy examines the claims of Clement Attlee and Margaret Thatcher to membership of that exalted band.

About Thatcher's qualification he has no doubt. She "transformed the politics of Britain - indeed Britain itself". But he is less sure about Attlee's right to a place in the pantheon. Admitting that he is changing the metaphor, he quotes the notion that "in 1945 the new consensus fell, like a branch of ripe plums" into the Labour leader's lap. "Mrs Thatcher forged her new consensus; Mr Attlee refined his".

The post-war zeitgeist, on which Attlee built his reasonable revolution, was brilliantly summed up in the title of Hennessy's account of the late Forties: Never Again. Attlee's achievement - metaphors being contagious - was not to turn the tide but to harness it. Identifying the nature of this historic success in no way diminishes it. It is no surprise that Hennessy, a fastidious scholar as well as a compelling writer, puts the way in which the world was changed into its proper context.

That is why it is surprising to read an endorsement of Nigel Lawson's view that Margaret Thatcher "set the political agenda for the next century". She did no such thing. On the day of her election it was already set out, item by item - a suspicion of "big government", antagonism to trade unions and a certainty that individuals freed from state bureaucracy would solve their own problems. Thatcher did not change the nation's convictions; she embodied them.

Hennessy was one of the first commentators to predict that Tony Blair would create "a commanding premiership" - a description he did not intend as an unequivocal compliment. That has certainly come about. Yet the "bit of freedom of information and democracy" in the Cabinet, for which he hoped, has not moderated the authoritarianism he identified.

Hennessy describes the new machinery of government - all its levers on the PM's desk - with the clarity and detail that has become his hallmark. But if Tony Blair joins Attlee and Thatcher in the ranks of PMs who presided over seismic change, it will not be because of his Promethean determination to steal fire from the gods. It will be because, in spring 1997, the British people wanted what he had to offer.

Greatness, in prime ministers, requires strength of purpose. The chapters devoted to 10 Downing Street's 12 post-war inhabitants make clear that strength comes in a variety of shapes and sizes. Attlee - Churchill's "modest man with plenty to be modest about" - had, in the words of one civil servant, "a terribly difficult team to drive... [but] he dominated them". Harold Wilson - although party unity was "the single consistent aspect" of his leadership - imposed his will at moments of crisis. The decision not to devolve the pound (his biggest mistake) was taken after consultation with two colleagues. The rest of the Cabinet, some of whom would have argued for the wiser option, were merely informed.

Poor John Major never had the chance to be strong. His party was so bitterly divided and - after the EMS débâcle of 1992 - so obviously doomed, that his authority was never respected. But on "sleaze" he could, Hennessy reminds us, "have been more Attlee-like in dispatching [erring] ministers to the back benches". Hugh Dalton celebrated Attlee's success in 1945 with the cry: "and a little mouse shall lead them". In 1947, when Dalton foolishly allowed the contents of his budget to leak, Attlee immediately accepted his resignation. The mouse roared quietly.

The chapters on No 10 from Attlee to Blair are more concerned with premierships than premiers. That makes them less biography than history. They are also immensely entertaining. Hennessy expresses his gratitude to the people who made writing The Prime Minister "fun". The pleasure shines from the pages.

Fun and scholarship are not incompatible. The part that analyses how the premiership has changed, and what alterations are necessary, is masterly. Hennessy destroys some romantic illusions. The monarch does not appoint the PM. He or she waits to see who can command a majority and then performs the ritual of invitation to form a government.

It is not the only "myth" Hennessy examines. Andrew Adonis, education adviser to Tony Blair, applies that description to the notion that the PM's workload has increased to a point that puts good government in danger. Adonis compares Gladstone's diary with Blair's, but, as he should know, the problem is increased complexity, not added hours. As a result, PMs have to rely on advisers such as Adonis to guide them through the policy maze.

In fact, he and his colleagues are the problem. A "commanding premiership" amounts to presidential powers, without checks and balances. Since the PM cannot become an expert on education, he takes advice from Adonis and, in his presidential way, imposes it on colleagues. Unfortunately, Adonis has written a book that rejects much of the education policy on which New Labour was elected. By taking his advice, the Prime Minister makes a nonsense of his manifesto and mandate. It is all the result of what Hennessy calls "excessive prime-ministerialism". The Prime Minister ought to be required reading in Downing Street.