Michael Brown: Why Cameron wants to delay Brown's succession

The longer he remains as Chancellor, the more humble pie he will have to eat

When David Cameron assumes the leadership of the Conservative Party later today the immediate attention will focus on his first outing at the dispatch box tomorrow against Tony Blair at Prime Minister's Questions. But, ultimately, it will be his battles against Gordon Brown that will determine his fortunes at the next general election.

Mr Cameron is in the strange position of being the first Tory leader in modern times who knows, for certain, that however brilliant he may be, without a single vote even being cast at a general election, he will definitely not be the next Prime Minister.

Mr Brown has already determined the successes and failures - mostly failures - of the careers of several of his Tory opponents. His decisions, more than Mr Cameron's, will probably determine the success or failure of the new Tory leader. Mr Brown has so far seen off six opposition shadow chancellors. Ken Clarke, Peter Lilley, Francis Maude, Michael Portillo, Michael Howard and Oliver Letwin have all held the post before George Osborne took over in the summer.

Mr Howard was the singular success who actually profited from his period shadowing Mr Brown - ending up Tory leader as a consequence. The new Tory leader will console himself that, unlike his colleagues who shadowed Mr Brown at the Treasury, he is likely to remain in his post for the duration of Mr Brown's tenure at No 10 - however long that may be.

With luck - and, like Mr Blair and Margaret Thatcher, Mr Cameron appears to have this essential political commodity in spades - there will be no further Tory leadership contest for at least a decade. After four leadership contests in the past eight years (three within the past four years) Tories have finally grown weary of such events. Whatever the outcome of the next general election, Mr Cameron is there to stay for many years and will be the most durable personality across the political landscape for a generation ahead.

Mr Cameron's first private dilemma is to decide whether it is in his interest to co-operate with Mr Brown in speeding up the demise of Tony Blair. If he displays the star quality his supporters believe he possesses and that translates into a consistent run of Tory opinion poll leads in the early part of 2006, the local elections next May could see a meltdown for Labour. This could renew an outbreak among Labour MPs of "time for Tony to go" by next summer. If the tumult becomes deafening, Mr Brown might even be installed as PM before the end of 2006.

But there is much to be said, from Mr Cameron's point of view, in lending whatever crutch is necessary to Mr Blair to keep Gordon waiting until the bitter end of this Parliament. This may already account for why he appears ready to establish a record of supporting the tattered remnants of Mr Blair's reform agenda - even in the division lobbies - thereby fomenting anger among left-wing and Brownite Labour MPs who have lost their appetite for more private sector involvement in public services.

A continuation of the Brown/Blair schism can still do nothing but good for the new Tory leader and too early a transfer of power to Mr Brown means that he could regain the initiative from Mr Cameron as the new kid on the block. A new prime minister who eschews the grandeur of office might yet refresh the Labour Party. Mr Cameron may also have a harder time against Mr Brown than Mr Blair, although somehow Mr Brown's tired steamroller approach to Mr Osborne yesterday was not as intimidating as it was to Tory shadow chancellors in previous years.

And the longer Mr Brown remains as Chancellor, the more humble pie he will yet have to eat. Mr Brown glossed over his over-optimistic forecasts of nine months ago and arrogantly refused even to nibble on the portions laid out for him by George Osborne on his growth and deficit forecasts.

So Mr Cameron should hope that Mr Blair limps on, forcing Mr Brown, as prime minister, to use the fifth year of this Parliament before going to the polls. Nothing is more guaranteed to put a government on the defensive than unplanned events and the ticking of the electoral clock - as John Major proved in 1997.

Mr Brown is looking ahead to the period 2009/10 with upbeat assessments for growth and borrowing. His aim, which he tried to reinforce yesterday, is to gamble on securing his own economic legacy in order to turn it into a political inheritance. In the meantime, Mr Cameron's case will be to prove that Mr Brown is actually digging his own grave. At which point, Mr Brown might even sacrifice his own current status as Labour leadership front-runner and suffer the fate that awaits David Davis later today.

mrbrown@talktalk.net