John Rentoul: Dave? Terrific. (But he doesn't have a chance)

No matter how good he may prove, Cameron has an impossible task

Yes, David Cameron is terrific. Even better than most people thought. He can name his favourite Smiths album without a moment's hesitation (The Queen Is Dead). He has poise and good judgement. He can hold his own against Tony Blair in the House of Commons, the first Conservative since Kenneth Clarke (as Home Secretary in 1992-93) to do so. He is green, and hence the potential darling of the anti-war liberal middle class. He doesn't stand a chance.

First, the numbers. The sacred text of British politics has just been published. It ought to be called "All Mr Cameron Needs to Know", but it is in fact called "Appendix 2: The Results Analysed" by John Curtice, Stephen Fisher and Michael Steed. It is to be found at the back of the equally racily titled The British General Election of 2005, by Dennis Kavanagh and David Butler.

It makes gruesome reading for any Conservative. The party needs to be 12 percentage points ahead of Labour in the opinion polls in order to win a majority in Parliament. That figure may be reduced when constituency boundaries are redrawn, but this will "far from eliminate" Labour's advantage, according to the authors. Nor will they affect the unusually wide range of results that would produce a hung parliament. If there had been this many Liberal Democrats and others at almost every election since the war, the result would have been a hung parliament. It looks fairly easy for the Tories to deprive Labour of its majority next time, but Brown starts with the added electoral bonus of not being the Man Who Took Us to War. And the Tories need to be 6 points ahead to have more MPs than Labour in a hung parliament.

Then there is the politics. The numbers can be overcome. For years in the 1980s and 1990s, wise heads said: "Labour can't win", "needs a bigger swing than any since the war" and "time to change the voting system". Then along came Tony Blair, whose landslide carried away all the settled assumptions about voting behaviour. If the politicians change enough, people will vote differently.

So the question for David Cameron is whether he can change perceptions of the Conservative Party enough to overcome Labour's built-in advantages.

Gambit one: going green. Friday's launch of Cameron's "quality of life" policy review puts off the "tough" decisions he says he will take - almost the first thing he said in answer to any question was "18 months". For substance, therefore, we have to go back to his article in The Independent on 1 November, which prompted environmentalists to hail him as the best green thing since the last great green hope, a position filled successively by Margaret Thatcher, Jonathon Porritt, the Prince of Wales and Tony Blair.

What excited them was that he promised legally binding limits to carbon emissions. "This will bind future governments into action," he wrote. Oh no, it won't. No government can bind its successors. The automatic annual increases in petrol tax, for example, were abandoned as soon as they became politically painful. Cameron also wrote that "joined-up thinking" was needed. "One Whitehall department ... wants carbon reduction, another wants more roads and airport runways." The clear implication was: no more roads and runways. We shall see.

The Prime Minister had a reply at the start of this year when pressed by select committee chairmen on his green record. "Hands up around this table: how many politicians," he asked, "would vote to end cheap air travel?" Only one put his hand up, and he was Richard Allan, the Liberal Democrat MP for Sheffield Hallam, who was standing down at the election. Or, as one of Blair's earthier aides put it after the appointment of Zac Goldsmith, the billionaire tycoon's son, as Tory green adviser: "How do you think the voters will respond to a series of nobs trying to deprive the country of cheap flights and the right to drive?"

Cameron's second gambit is to get more female MPs. He proposes everything short of all-women shortlists, on the respectable principle that official discrimination against men is the wrong remedy for unofficial discrimination against women. But the Labour Party's experience is that nothing else works. So Cameron is not only playing catch-up, but he has no gears on his carbon-fibre mountain bike.

Gambit three: support Tony Blair's schools reforms. Well, it brought the Commons to life. It involves some fascinating, intricate politics. Cameron's attempted embrace forced Blair to dodge to the left at Prime Minister's Questions last week - possibly the most keenly anticipated and over-analysed session since the televising of Parliament.

Blair said: "I think that if schools are free to bring back selection at the age of 11, that would be regressive for our country." A mere 44 hours later, Cameron swerved to the left too on the Today programme. "I do not want a return to the 11-plus," he said. He did not believe that giving schools control over their own admissions would lead to the "binary division of children", but for the first time said that a Tory government would give such powers to schools "progressively". The pedals on his bike are already going backwards.

Some on the Labour side appreciate that this is an opportunity rather than an embarrassment. "Long-term political change is embedded when you convert your opponents," writes Sunder Katwala, the head of the Fabian Society, in this month's Prospect magazine. "If David Cameron makes a serious attempt to modernise the Tories, Labour should welcome it."

Most importantly, that means that Gordon Brown should welcome it. As long as the Chancellor hugs the Prime Minister even more tightly than Cameron does, there is no reason why, on public service reform, the voters should prefer the Tories to Labour. Hence the significance of Brown's interview on the morning of Cameron's election as Tory leader: "I don't think anybody should be in any doubt that not only will the reforms continue, but in future years they are going to have to be intensified."

That is not to say that Cameron is pursuing the wrong strategy. It may be the best available, just as he is the best available leader. But neither is enough yet to end the Tories' losing streak.