Only one thing might tempt voters to back Mr Cameron

The party's conference in Manchester this week provides ample illustration of this gap between conservatives and Conservatives. Activists will, naturally enough, spend a good deal of time celebrating the life of their most successful peacetime leader, Margaret Thatcher - and not a few of them will be muttering about how much better she was than the current leadership. Except on a few social issues, however, Lady Thatcher wasn't much of a conservative at all, but a radical Whig and vigorous advocate of Manchester school economics.

Another giveaway will be the number of empty seats. There has been a substantial fall in the party's membership over recent years. According to Central Office, which was initially reluctant to confirm the figures, it now stands at 134,000 - about half the number it was when David Cameron became leader.

A large number of these vanished members are now to be found within the ranks of Ukip, and they are certainly drawn from the more conservative - you may prefer reactionary - section of the party. For all Nigel Farage's insistence his party is picking up disaffected Labour voters, and people who have never previously supported any political party, the overwhelming majority of his members are disillusioned Tories.

That is a huge headache for Mr Cameron, because, according to private polling conducted for the Tory peer Lord Ashcroft, loss of support to Ukip could let the Labour Party seize 32 marginal seats currently held by Conservatives. At the same time, Labour has finally obtained a respectable-looking lead. A YouGov poll at the weekend found the party has pulled 11 points clear of the Conservatives, to 42%, which is also more than the 40% the Coalition parties can muster between them.

Ed Miliband may still have dismal approval ratings, even among his own party's supporters, but he was generally thought to have had a successful conference. His list of policies, such as free childcare for all primary school children, reversing the VAT increase and child benefit cut, a huge housebuilding programme, and fixing energy prices may be ludicrously unaffordable, ill thought out and possibly even illegal, but there's no doubt they are likely to be popular.

Predictably enough, the Conservative response to this state of affairs has been slightly muddled. On the one hand, the party is making a - in my view, futile - attempt to win back voters who have been attracted to Ukip, by banging on about immigration and having promised a referendum on the EU. On the other, it is, in a thoroughly unconservative fashion, increasing public spending. Silliest of all is the populist, but idiotic, cheap home loans scheme being brought in early, on the basis that the British public, against all the evidence, see rising house prices as an index of prosperity.

The Prime Minister will also be hoping social conservatives who were annoyed by legislation on same-sex marriage will be mollified by the long-awaited arrival of a tax concession for married couples. I'm afraid that on all these points he is, contra Oakeshott, putting his hope in the possible, indeed the improbable, rather than the actual.

The section of the right which has decamped to Mr Farage's banner is, to put it bluntly, not going to be won over by anything the Prime Minister does, because they have already decided they don't like or trust him. In any case, this section of the electorate may be sizeable enough to lose Mr Cameron the election, but it is not on its own large enough to win it. And ramping up the rhetoric on immigration, crime and cutting benefits (all things which Ukip voters are much more interested in than Europe) runs the risk of alienating many voters in the centre, who find it easy to see the Tories as the nasty party.

Only one thing might tempt both disaffected Tories and undecided swing voters to hold their noses and support Mr Cameron. And it is, happily enough, the conservative prescription of the late Professor Oakeshott. It is to point out the facts and argue against fanciful solutions. It is to emphasise reality, and to ridicule utopian promises.

I expect Mr Farage's party will do well in the European elections. But at least some of its supporters could probably be persuaded to vote Conservative if, when the General Election rolls round, there is a clear danger voting Ukip would put Ed Miliband in No 10.

Similarly, the Labour leader's unpopularity with many undecided voters, and the memory of his party's catastrophic mishandling of the economy, might be enough for them to stick with Mr Cameron. For the Coalition Government can point to a real, and solid, achievement, even if it is not very spectacular, or the bright sunlit uplands we might all have preferred. The economy is in recovery. There are more people in work than ever before. There have been some cuts in public spending, and some attempt to tackle the deficiencies of the benefits system.

Mr Cameron can fairly and honestly say the Coalition's policies have worked, and have got us as far out of the hole the last government dug as they could have been expected to. And his great advantage will be to contrast that real, if modest, success with the pipe dreams of the Labour Party.

The Tories may not have actually succeeded in cutting overall spending or debt yet, but it is now obvious the policies which were being advocated by Mr Miliband and Ed Balls would have made matters very much worse. Mr Balls has so far produced spending pledges of more than £30 billion - all of which he claims will be funded by a "tax on the banks".

Even if many of us feel either that the Government's measures have not gone far enough, or that they have been unduly painful, Mr Cameron can at least present a credible tale of improvement, while Labour is still peddling a fantasy. He can't really claim it's been an unalloyed triumph, but the British public may be realistic, and conservative, enough to see it as the best we could have hoped for.