‘The plates are moving,” John Prescott remarked last year. Had he specified “tectonic” it would have aided our comprehension, but the remark was perceptive. Every few years, strains beneath the political crust resolve themselves in massive changes in the landscape.

David Cameron’s election as Conservative party leader will hopefully render the Tories unrecognisably attractive and electable. The seismic effect of his shift to the centre has also intensified the rumblings that shake Charles Kennedy and Tony Blair. Cameron hopes that the upheaval might send some Liberal Democrat MPs sliding over to the Tories, and on Friday he issued a mischievous invitation to them to defect.

Kennedy cannot survive for long and I hope that early in 2006 he will take advantage of a quiet moment to leave his post, apparently of his own volition. In two successive elections his party has increased its share of the poll and its seats. That record gives him the chance to leave with dignity, but it is not a reason for staying.

Nor is the predictable mayhem among the Lib Dems that will follow his departure. Menzies Campbell, the party’s deputy leader, commented last week that the Lib Dems have a wealth of talent in parliament. That is the problem. It is far from obvious whom they should choose and in which direction they should head.

Campbell has the gravitas to be leader. He looks like a Tory and might scoop up Conservative votes. But traditional Toryism is in collapse, which is why the Conservatives have made the historic decision to change. Anyway would the Lib Dems seriously elect a man nearly twice as old as Cameron?

Simon Hughes (the party’s president) offers a lurch to the left, away from the overcrowded middle ground. The Lib Dems have long been the only big party overtly committed to higher taxes and opposed to the Iraq war. Since Cameron’s election they also hold the monopoly of opposition to student top-up fees. But Hughes looks a decidedly dated radical. In any case, the other brains in the party want to move in the opposite direction.

One of them, Mark Oaten, the shadow home secretary, seems to be self destructing, torn between appearing loyal to Kennedy and looking like he is ready for the leadership contest. To my mind the most impressive candidate is David Laws, spokesman on work and pensions and co-editor of the Orange Book. That collection of essays urged the party to adopt economic liberalism and free markets, to work for limits to Europe’s powers, to resist the nanny state but to recognise the efficacy of prison in protecting society from criminals.

At 40 years of age, Laws looks good on television and sounds eminently reasonable. But he has yet to show charisma to match Cameron (or even Kennedy before the poor fellow became burdened by the leadership). Party activists have not made the same intellectual journey as the bright young things in parliament. It will be hard to convince them to elect, like the Tories, a leader with looks, soundbites and policies inspired by Blair.

Kennedy has been his party’s John Major. He has remained bravely indecisive, commanding his party’s catamaran with a foot on each hull as they move apart. After the unavoidable bust-up to come, people will look back nostalgically on his reign. In truth, the party’s dichotomy must be resolved and the sooner the better. The difficulty is that in a political party with competing talents as well as philosophies, it is doubtful the next leader can sort it out.

Cameron has left the field clear for the Lib Dems on top-up fees, but it is well worth it for the sake of greater consistency in Tory policy. In other ways he is applying pressure that undermines his third-party rivals. A picture is worth a thousand words and his choreographed bicycle rides have more eloquently communicated a concern for the environment than all Kennedy’s speeches.

In due course, Cameron’s environment strategy will bring dilemmas. He has set up a working group headed by John Gummer, who is much given to virulent criticism of America’s failure to sign the Kyoto accords. The Conservatives must not become anti-American. The group also includes Zac Goldsmith. The highly articulate environment campaigner has the panache of Sir Jimmy, his late father, and looks that make women swoon. It was almost too good to be true when a while back he joined the Tories.

That, too, was a sign the plates were moving. But he is doggedly anti-nuclear power, another thing the Conservatives cannot be.

The Tory strategy has already moved the ground beneath Blair’s feet. Cameron’s decision to support the prime minister’s schools reforms is delightfully destabilising. The government stands little chance of passing its legislation without Tory support. Diverse elements of the Labour party object to granting trust schools relative autonomy over admissions policy and budgets, thus diminishing the role of local education authorities. Cameron has left himself room for manoeuvre.