Perhaps it may not be so easy after all for David Cameron to win an overall Commons majority. The latest Populus poll for The Times, undertaken over the weekend, underlines the obstacles. Both main parties are down a point. The Tories are, at 39 per cent, at the lower end of their recent range, and Labour, on 29 per cent, at the upper end of theirs.

But the warning signs are clear. According to the UK Polling Report’s ready reckoner, which assumes a uniform switch of votes between the parties, these figures would give the Tories a majority of only two.

No wonder that the number expecting a Tory overall majority has slipped from 57 to 50 per cent in the past month, the lowest level since the question was first asked in April. By contrast, the number expecting a hung Parliament with no overall majority has risen from 17 to 26 per cent. However, 65 per cent still expect the Tories to be the largest party, against 27 per cent for Labour.

Likelihood to vote has fallen among the Tories, possibly as part of a backlash against mainstream parties after last week’s stories about MPs’ expenses. By more than a two to one margin (68 to 30 per cent), voters do not believe that, in light of the clampdown on expenses, MPs should have their pay increased to recruit “good people” and keep existing ones in the Commons.

The Tories have suffered slightly from last week’s shift by Mr Cameron on Europe after the final ratification of the Lisbon treaty. Support for other parties has risen by two points to 14 per cent, with the UK Independence Party up from 2.3 to 4.3 per cent. Apart from the two months around June’s Euro elections, this is the highest level since 2005.

The numbers are very small, but aggregate data over several months suggests that support is highest among working class groups and older people. Forty-eight per cent back the Cameron line that “it would be pointless to have a referendum on Europe unless specific further changes in Britain’s relations with the EU were being proposed”, against 46 per cent believing there “should be a referendum early in the next Parliament on the general issue of Britain’s relations with the EU”. However, Tory voters disagree with their leader’s line, with 59 per cent backing an early referendum against 37 per cent calling it pointless.

The Tories remain very well placed to oust Labour next spring, but a minority Cameron administration is a distinct possibility.

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