David Cameron, defender of the Union. That the leader of the Conservative and Unionist Party should choose to emphasise his support for the Union in an interview with The Herald, published today, is revelatory in the context of the shifting political landscape of Britain. There is a school of thought that, should he lead a Conservative government at Westminster, it would be in his interests to exploit tensions with the SNP administration at Holyrood in such a way that the endgame was the advent of an independent Scotland. Labour would be denied the rump of MPs it depends on at present and the Tories would effectively enjoy a natural majority of support in England.

The prospect of securing long-term power under that scenario must be attractive but Mr Cameron is having none of it. He has been at his weakest when trying to define himself and what his party stands for. He still has a great deal of convincing to do on that score. But he could not be clearer in his commitment to the Union, saying at one point: "I don't want to be the Prime Minister of England, I want to be the Prime Minister of the United Kingdom."

There is an advantage to be gained from being clear and consistent on the Union and contrasting that position with the mess Labour has allowed itself to get into over Wendy Alexander's challenge to the SNP to call a referendum now on independence even although there was no convincing case for doing so, either on the basis of Nationalist policy (set out in the party's last Scottish election manifesto) or Gordon Brown's position (somewhat at odds with that of the Labour leader at Holyrood).

But Mr Cameron, who will address the Scottish Tories at their annual conference in Ayr today, must be aware of the nuances of politics north of the Border to avoid any traps of his own. Annabel Goldie, the Scottish party leader, and her colleagues have aligned themselves with the SNP to the intended benefit of both. The Scottish Tories have played their part in keeping Mr Salmond in power and, in return, have won government backing for policies on business rates, law and order and drugs. There is a different way of doing politics under the devolution settlement and its propensity to deliver coalition or minority government.

A consensus appears to be emerging that Scotland should have greater fiscal autonomy and Mr Cameron hints that he could live with that. He believes that the Barnett formula has had its day and needs to be replaced. He is probably correct. Although it has become less advantageous for Scotland by dint of growing convergence in spending gains, it is based on an outdated assessment of need. There would be losers as well as winners in any replacement. Could his solution keep both the Scots and the (traditionally Tory) English public who complain about subsidy junkies happy? It will be a difficult balancing act. As in other policy areas, we must await the detail.