Nobody could accuse Peter Kellner of YouGov of being a closet Tory. Thus an upbeat assessment he has offered today of Conservative polling prospects is all the more encouraging. In some ways the timing is odd. After the budget the Conservatives were practically neck and neck with Labour in the polls but after the Maria Miller debacle they have slipped back a little on most recent polls to a gap of around six per cent.

Mr Kellner says:

At times like this, we should filter the froth from the fundamentals: the short-term pressures from the long-term forces. The Conservatives’ latest dip bears all the signs of a brief, news-driven, wobble arising from the way Cameron handled Maria Miller’s resignation saga. Before long, the party’s fortunes should revive.

Among, the factors Mr Kellner regards as “the fundamentals” is that “the economy is improving – and voters are noticing.” The Conservative “have opened up an 11-point lead” over Labour on which Party is best at managing the economy.

Another “fundamental” is leadership. David Cameron’s personal rating, which despite having slipped of late to minus 16 is still well ahead of both Ed Miliband – on minus 26. When asked who would make the best Prime Minister Mr Cameron is 16 points ahead, of Mr Miliband.

If history is a guide a political party can be behind on one of these factors – economic competance of offering the leader who would make the best PM. But not both.

Mr Kellner says:

To be sure, parties can still lose elections when they go into an election ahead on economic competence or personal leadership. In October 1964, Gallup found that the Tories enjoyed a 13-point lead over Labour when people were asked which would be better at ‘maintaining prosperity’ – yet Labour narrowly regained power. Six months before the 1979 election, James Callaghan trounced Margaret Thatcher by 50-26% when voters were asked who would make the best Prime Minister – yet this failed to save Labour from 18 years of opposition.

However, I can find no example of a party losing an election when it is ahead on both leadership and economic competence. If Britain’s recovery is sustained (especially if living standards start to improve) and Cameron is able to maintain his lead over Miliband, then we are likely to see a swing back from Labour to Conservative over the next 12 months – as we have every time in the past half century that a Conservative Prime Minister has led his or her party into a general election.

Past performance does not necessarily predict future results, as they say in the financial small print. But surely there is already something about Labour’s poll lead which is defyinig political gravity. If that is the case now it will be still harder for Labour to retain an opinion poll lead in a year’s time as the economy grows. In particluar Labour’s attack on welfare reform will be more clearly seen as misjudged as unemployment falls.

Mr Kellner allows himself a caveat. While he does not think a UKIP victory in the Euro elections would in itself scupper Tory prospects it might if it promptted Tory MPs to attack David Cameron and thus persuade the electorate that the Conservatives had become a divided party. Maybe. But a UKIP victory in the Euro Elections is so widely predicted any claims to be shocked by it coming to pass would be rather synthetic.

In any case would it not also pose certain questions for the Labour Party. Even in 1999 the Conservative won the Euro Elections under the embattled leadership of William Hague. In 1989, Neil Kinnock’s Labour Party triumphed at the polls. Those wishing to protest against the Government were the mpst motivated to tun out and vote. If UKIP win then Mr Miliband will also have his critics to face.