The Conservative Party conference opened yesterday in a more restive mood than might have been anticipated. This was partly due to the impact of Labour’s eventful jamboree in Manchester, which had a surreal soap-opera quality yet was compelling drama. The Prime Minister’s oratorical excellence established a new standard not just for Gordon Brown and his Labour rivals, but also for the man who has revelled in describing himself as “Blair’s heir”.

The peace in the Labour Party is uneasy but the fear of mutually assured destruction makes unlikely another Brownite attempt at regicide.

The question is, therefore, whether David Cameron is ready for a war on two fronts, one with ministers who will leap on the slightest mistake that he or his associates make and another with those in his party who want to see some firm policy placed on the table. The artificial storm over Oliver Letwin’s essentially inoffensive remark that there was no limit to what the private sector should be allowed to do within the NHS shows how brutal the Labour Party will be in its quest to remain in office. The difficulties that Mr Cameron has created for himself over tax cuts, on the other hand, are an indication that he has yet to make a distinction between coherent principle and necessary practice.

No one expects Mr Cameron or George Osborne, his Shadow Chancellor, to publish today a plan for a Budget that might not be delivered until 2010. What is reasonable is to ask whether the Conservatives believe that the levels of tax and spending set out by the Treasury for the remainder of this decade and beyond are too high. The core principles of policy direction must be articulated even if the finer detail will have to wait. The notion apparently held by few in Mr Cameron’s circle that tax can be their “Clause Four” issue is risible. One does not need to be “right-wing” to want some of your money back. While the Tories fret over tax cuts, it is a certain bet that Mr Brown will find a way of cutting some taxes before the next election, making Mr Cameron look all the more foolish.

It is an inability to signal his principles, not the charge of “style over substance”, that should concern the Conservative leader. There is little point in him appearing in webcam broadcasts if he seems to have little of consequence to say. If he cannot state principles clearly, then the gibe that he is no more than “Dave the Vague” may stick even after he delivers on the policy detail. Mr Cameron referred in his talk to delegates yesterday to party renewal as akin to building a house — clearing the ground, laying the foundations and erecting it brick by brick. This is true, but most construction projects involve an architect’s plan for the finished product and a firm base on which to build.

In all this, the Tories might learn a trick or two from Senator John McCain, their guest speaker. The senator has established himself in the centre groud, as Mr Cameron hopes to, and he appeals to Americans who do not consider themselves partisan Republicans. He has managed this not by being ambiguous or slick but through taking public and sometimes unpopular stands of principle on the serious issues of the day and speaking with relentless candour to the elect-orate. Mr Cameron should aspire to be another Mr McCain, and not a re- incarnated Harold Macmillan.