The Adrian Mole generation

David Miliband (Labour), David Cameron (Tory) and Nick Clegg (Lib Dem) lead the new wave in politics

The unceremonious removal of Charles Kennedy as leader of the Liberal Democrats had nothing to do with alcohol and everything to do with the revival of the Conservative Party under David Cameron. By his own admission, Kennedy had been struggling with alcoholism for at least 18 months and his colleagues had consistently covered for him. They were prepared to do so only as long as the Conservative Party proved itself to be even more incoherent and divided than they were.

The Sheffield MP Nick Clegg, an important figure in Menzies Campbell's leadership campaign who has been tipped to become a future leader himself, is unequivocal. As soon as Cameron came on the scene Kennedy had to go. "The crisis about Charles Kennedy's leadership was a response to the changing geography of British politics," he told me. "The centre ground was becoming crowded and we were not punching above our weight. If the leadership election comes out in the right way we will be better-equipped to stop Cameron stealing the liberal mantle from us."

In one month David Cameron has become the driving force in British politics and the other two parties have been forced on to the defensive. Tony Blair has been quickest to react to the threat, and the reshuffle he began trailing in interviews in the past week will bring a further injection of youth into a government that looks sluggish and old-fashioned compared with the vim and enthusiasm of Cameron and his lieutenants.

We are witnessing a significant moment in British politics, with the passing of the political baton from one generation to the next in each of the three main parties. This is never a painless process, but in its hunger for victory, the Tory party has so far allowed the transition to happen with the minimum of fuss. The Liberal Democrats and Labour are not yet prepared to go as far in handing over the leadership itself, but power is shifting.

Blair is adamant that new blood will be necessary to counter the Cameron threat. His praise for the next generation of new Labour politicians, in advance of the reshuffle, has inevitably been interpreted as a dig at Gordon Brown, but on one level the Prime Minister was simply recognising the growing need for the party to renew itself while still in power. It has long been possible to interpret every utterance by Brown or Blair as evidence of a split, but the Chancellor would not disagree that David Miliband and Douglas Alexander are critical to the future of any Labour government.

It may seem odd to suggest that the Liberal Democrats are going through a similar process of rejuvenation when they look determined to transfer the leadership from a relatively young man of 46 to someone a year off from the state retirement age. But it has been noted that Nick Clegg and David Laws, "Young Turks" of the Lib Dem right, have lined up behind the older man. As one senior Liberal Democrat notes: "Ming Campbell is not known for his grasp of domestic politics, so there may be a calculation that there will be scope for the younger members of his team to drive that agenda." The second candidate to declare, Mark Oaten, is similarly in his early forties, as is his most high-profile supporter, Lembit Opik. Although they will almost certainly lose in the leadership ballot, both men are guaranteed a future as prominent members of their party's front-bench team.

The recent events have confirmed the emergence of a generation of politicians young enough to dominate the scene for at least the next decade. Indeed, in 2016 Cameron, Miliband and Clegg will all be younger than Tony Blair is now.

Born within 18 months of each other, they form an oddly homogeneous group of fortyish, Oxbridge-educated politicians more remarkable for their similarities than their differences. All three have been involved in front-line politics since their twenties: Cameron as an adviser to Norman Lamont and Michael Howard, Clegg as an adviser to the Tory Leon Brittan when he was a European commissioner, and Miliband as an influential architect of the new Labour project. All three would describe themselves as social liberals and all three are convinced of the power of the market to transform public services. At the same time, they have far more in common with each other politically than they do with many MPs from their own parties.

If we widen the circle further, it is possible to identify a swathe of senior politicians who have recently turned 40 or are just about to: David Laws and Lembit Opik in the Lib Dems, Michael Gove and Boris Johnson in the Conservatives, and Labour's Ed Balls and Douglas Alexander all fall within this age bracket. In a sense, it is no great surprise that men in their late thirties and early forties should begin to dominate their profession of choice, but in politics it has generally taken a little longer.

What drives the essentially moderate and unthreatening politics of this new generation? We know, for example, that the political event that dominated the thinking of the baby boomers who created new Labour was the Tory landslide of 1983. The surprise victory of John Major in 1992 has a similar iconic status for Labour politicians of the younger generation, who would have been in their mid-twenties at the time. The event also has resonances for the younger Tories. Cameron remains deeply scarred by the experience of working within a weak and promptly discredited government.

As someone who also turns 40 this year, I can claim a certain insight into the political psychology of this generation. David Miliband sees our generation as the last still obsessed with the cold-war divisions of left and right, but also the first to grow genuinely weary of those rigid distinctions. Our time at university (a time when most young people's personal politics are forged) was dominated by the fallout from the class-war politics of the miners' strike. The poll-tax riots demonstrated the limits of Thatcherism, and by the end of the century we were crying out for an ideological "Third Way" between the tired ideologies of the hard left and free-market fundamentalism. In the circumstances, it is perhaps not surprising that the politics of the Cameron generation is relentlessly centrist.

This is the Adrian Mole generation, almost exactly the same age as Sue Townsend's fictional diarist (who was born, according to his journal, on 2 April 1967). Like Mole, they are an ultra-conventional bunch, in their social attitudes as well as their politics. Such is the closeness of the younger MPs across the parties that some who have no political memory beyond Margaret Thatcher may be prepared to open up direct lines of communication and build strategic alliances. I know several members of the Tory and Labour front-bench teams who have already put out feelers to Nick Clegg, while Ed Miliband, usually thought to be to the left of his elder brother, says the MPs he finds most engaging are the Tories Ed Vaizey and Michael Gove.

This free-floating, non-ideological politics brings questions. The coming generation is undoubtedly bright, talented and articulate. But it could become an amorphous grouping of polite, if ambitious, young men if it fails to provide the radicalism and political definition to inspire disengaged voters. As it prepares for a long-term association with power, the generation represented by Cameron, Miliband and Clegg risks producing a political philosophy as anodyne as the Pink Brigade, the "radical group" set up by Adrian Mole aged 13 3/4 with the distinctly unthreatening manifesto: "War (we are against it), peace (we are for it)."