Labour should not be triumphalist. The next election is not yet in the bag. At present, the headline polls all point in the same, favourable, direction for Labour. But there are seven reasons for Gordon Brown to be cautious and not to assume that current ratings will translate into a big victory in November.

First, the polls could change. What matters is not the lead, but the level of each party’s support. Labour is on about 40 per cent, against 33 per cent for the Tories. If repeated, this would be enough for a Commons majority of more than a hundred. But, as recently as June, the two parties were level pegging on 36 per cent. And the margin of error is plus or minus two points.

Second, the Liberal Democrats often, though not always, come up in the polls during a campaign when they receive more coverage. And their sitting MPs are adept at exploiting tactical voting, to offset, if not halt, a national swing against them.

Third, as the invaluable UK Polling Report has noted, there should be an incumbency bonus for the 40-odd Tory MPs who won seats from other parties in 2005. On past form, they should do better than the national trend, especially at their first reelection attempt.

Fourth, regional variations could benefit the Tories, if the party is doing relatively better in the South, where there are many Labour and some Lib Dem marginal seats. And issues such as immigration and crime could also play well for them.

Fifth, calling an early election could backfire on Mr Brown. As I argued last Friday, the relevant parallel is not the postponement of the election in 1978, but Harold Wilson’s decision to call, and then lose, an election for June 1970, on the basis of a recent and short-lived upturn in Labour’s rating. Wilson ran a complacent “trust Harold” election. The risk now is that Labour relies too much on Mr Brown’s personal strengths and does not spell out what it would do in a fourth term: how far will public service reform go? That was the great gap last week. A strong mandate depends upon a clear and detailed programme.

Sixth, an effective counter-attack by David Cameron could establish a sharper identity about what the Tories would do in office. First signs yesterday were promising with a confident performance and several eye-catching policy proposals.

Seventh, the chief executive of Association of Electoral Administrators has warned of big practical problems with an early poll and the disenfranchisment of over a million voters.

None of these factors are decisive against an early election (hardly a snap one given the amount of speculation). But they should act as a brake against overenthusiasm. Admittedly, there is virtually no chance of the Tories replacing Labour as the largest party, and none at all of them winning an overall majority. This is because Labour distributes its votes more efficiently, with lots of small majorities, while the Tories pile up big majorities in safe seats. But a shift of a couple of points could threaten Labour’s hopes of a big majority.

An early contest would be counted a success for Mr Brown only if Labour increased its majority above its current 66 (around 45 after boundary changes). Anything less, and the question would be: why had Mr Brown called an election more than two years early?

Agenda for the week

Today

9.45-11.00am Public services debate, including Andrew Lansley, the Shadow Health Secretary, and Michael Gove, the Shadow Schools Secretary
11.15am-12.30pm Economic competitiveness debate, including George Osborne, the Shadow Chancellor
2.30-3.45pm Debate on fixing broken society, including Chris Grayling, the Shadow Work and Pensions Secretary
4pm-5pm Debate on childhood in Britain today, including David Willetts, the Shadow Skills Secretary

Tomorrow

9.45-11am National and International Security Debate including William Hague, the Shadow Foreign Secretary Shadow
11.15am-12.30pm Globalisation and global poverty debate
4pm-5pm Rebuilding Democracy including Nick Herbert, the Shadow Justice Secretary

Wednesday

9.30am Simon Mort, the conference chairman gives his final remarks
9.45-11am Quality of Life Debate
2pm David Cameron makes his closing speech to the conference

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