Pity the Tory candidate for mayor of London, if there ever is one. He or she will be mocked because David Cameron wanted someone else. Indeed, he did not want a Conservative at all.

That is the unhappy legacy of last week’s revelation that the Tory leader had pretty much persuaded Greg Dyke, the former director- general of the BBC, to stand against Ken Living-stone as an independent with Conservative and Liberal Democrat backing. The plan was scuppered and made public by Sir Menzies Campbell, the Lib Dem leader.

To put it mildly, Dyke was an unexpected choice for the Tories. When he was proposed for the BBC in 1999, William Hague, then Tory leader, called the appointment “totally unacceptable” because Dyke had given £50,000 to Labour and funded Blair’s leadership campaign.

Of course, times change and people, too. Dyke certainly feels little affection now for a government that forced him out of his job over the BBC’s reporting of its dodgy dossier on Iraq’s alleged weapons of mass destruction. But Dyke has not become a Tory. Nor is he politically savvy (as his downfall demonstrated) and one shudders to think into what farce the mayoral campaign would have descended as journalists daily elicited his views on Conservative policies.

The incident has rattled the party. Cameron’s judgment looks faulty. Admittedly it would have been a coup to announce that a former Labour donor was now the Tory candidate. But when it became clear that Dyke would not wear a blue rosette, was the Conservative leader right to think of fielding him as a nonTory?

Arguably the offer to Dyke merely confirms what has been known for a long time: that the party despairs of finding any big name to represent it in London. Nonetheless, the capital is supposedly where Cameron’s brand of politics plays best. A good result there is vital if he is to reach Downing Street. Are the Conservatives perhaps afraid to have their true level of support measured in a London-wide poll in the year before the general election?

The Tory spin on the unhappy event is that, responding to the public’s dislike of partisanship, the party is engaged in a new politics which can embrace compromise and coalition. Having tried in Commons debates to force Des Browne out of office on Monday and Gordon Brown on Tuesday, it was not the best week for the Tories to claim to have left yah-boo politics behind. But even if the Tory gloss on the embarrassing Dyke episode is unconvincing, it is true that the style of British politics is shifting under our noses.

One influence is the Tories’ recognition that elections are won on the middle ground. They now see that the 1980s were an aberrant period. When Michael Foot took Labour to the left, he gave Margaret Thatcher a chance to move to the right, like two children balancing each other on a seesaw. Once Blair had positioned Labour back in the centre, staying out on the right has marooned the Tories and brought them electoral disaster.

With nearly 6m fewer votes than they had in 1992, the Tories no longer rely on appealing to their core electors. The party wishes, as Blair did in the mid1990s, to build a big tent and has attracted illustrious nonConservatives to work in its policy groups.

Having little hope of winning parliamentary seats in any large English city apart from London, the party has already entered coalitions with the Lib Dems to run the councils in Birming-ham and Leeds. It was a practice frowned on by Michael Howard, but Cameron recognises that by sharing in power the Conservatives are on a fast track to rebuilding their membership and credibility in urban areas.

Despite now enjoying a fairly consistent and sizeable lead over Labour in the polls, the Tories remain doubtful about winning the next election. They still struggle to get as high as, let alone above, a 40% level of support. Cameron has semiofficially abandoned hope in Scotland with his half-decision to create a separate party north of the border. It is hard to identify swathes of seats in the Midlands and northern England poised to switch to the Tories, as they must to give the party an overall majority. If the Tories’ lead in the polls simply increases majorities in southern England they will not take office, not on their own anyway.

After the election Cameron may be in the business of coalition building in parliament and it will be useful to show that his party can be a willing and reliable governing partner at other levels of government.

Other things are happening well outside the Tories’ sphere of influence. The extraordinary coalition of Ian Paisley and Gerry Adams in Northern Ireland must influence political psychology across the UK. Events in Scotland next month could shift our thinking further if the Scottish Nationalists become the largest party. It may lead to another improbable coalition.

Under proportional representation there is no reason why the party with the most seats should be in government. Yet if the SNP has a clear lead, it could spark outrage if Labour and the Lib Dems ignore the electors’ verdict and go on ruling. The two parties between them invented the Scottish parliament and have run it since. So if the SNP’s Alex Salmond becomes first minister it will be no ordinary change of administration.

On the face of it, a coalition between the Nationalists and Lib Dems looks impossible because the former are committed to calling a referendum on Scottish independence. But the SNP should seize the opportunity of office at almost any price. Given that it would on present trends lose the referendum heavily, it ought to ditch the commitment in order to enter a coalition.

Instead the parties might agree to seek more powers for the Scottish parliament. The SNP would hope that Westminster would reject that demand and then there could be a referendum on that decision, which would probably attract massive popular support. Having whipped up national fervour, and especially if by then there were a Tory administration in London, the SNP would have a better chance of calling a plebiscite on independence with some hope of success.

After May’s elections, most Scottish local authorities will also be coalitions, because for the first time they are being elected by proportionate voting. Somewhere there may even be some Scottish Tories sharing in power.

In the Scottish parliament a coalition of Nationalists and Lib Dems should be able to agree to introduce local income tax. That experiment could have seismic effects across the UK, because it would dramatically increase the autonomy of local government, ushering in devolution of a different sort.

So while, as last week’s debates demonstrated, the House of Commons looks and sounds the same as ever, all around it British politics is changing even faster than our climate. Cameron thinks that he will be better placed than Brown to take advantage of the new dynamics, since the chancellor finds it hard enough to work with his own party let alone with others.

But Cameron must be discouraged by Campbell’s rejection of the Dyke plan. Hopes of matchmaking with the Lib Dems are off to a poor start. If after the general election Brown and Campbell draw on their common roots in Fife and do a deal, proportional representation in Westminster elections could be the Lib Dem price. After that the Conservatives’ only hope would be that — very rarely — they might be allowed to share in office.

Cameron’s handling of the Dyke incident was clumsy. But it was more than just an ill-thought-out wheeze. The Tory leadership has been reflecting deeply on the shifting tectonic plates of United Kingdom politics.

While the party talks about winning an outright victory, other gloomier scenarios are at least as likely. In one, the Conservatives urgently have to find new ways to do business with other parties in local government as a prelude to doing a deal at national level. In another scenario the electoral system changes and the Tories have to woo new partners because otherwise they will be in opposition for ever.

michael.portillo@sunday-times.co.uk

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