John Curtice: The polls agree on one thing: Lib Dems are making progress

Two very different pictures of this election are emerging. One is supplied by conventional pollsters, most of whom undertake their surveys by telephone. According to them, including NOP's polls for this paper, Labour is winning comfortably. Over the past week, they have, on average, put Labour six points ahead.

Two very different pictures of this election are emerging. One is supplied by conventional pollsters, most of whom undertake their surveys by telephone. According to them, including NOP's polls for this paper, Labour is winning comfortably. Over the past week, they have, on average, put Labour six points ahead.

The other picture is supplied by the internet pollsters, for whom this election is their first full outing. The pioneers of this technique, YouGov, have - on average - put Labour only two points ahead in recent polls. Other internet polling conducted by academics at Essex University also gives Labour only a two or three point lead - and even puts Labour behind among those certain to vote.

That divergence is not new. YouGov has been disagreeing with its rivals about the strength of Labour's position for more than a year. But if this pattern persists until 5 May then not only will this election make or break Tony Blair's hopes for a third term, it will also make or break the future of internet polling.

At this stage no one can be sure who is right. For example, YouGov feels people are more honest on the internet and that might help explain why it has more Tory voters. However, conventional polls report that it is Labour rather than Tory voters who seem to be the more reluctant to declare their affiliation.

Still, even if YouGov is right and Labour is only two points ahead, that would still be enough for a substantial Labour majority, albeit not a landslide. There is a large pro-Labour bias in the electoral system, a bias that will only be significantly reduced if the Conservatives record an above-average performance in marginal seats.

But two polls conducted in the past week by ICM in key Labour/Conservative battlegrounds give no hint of that happening. At present there is a pro-Tory swing since 2001 of just one point in those seats, little different from the 1.5 point swing implied by the average of the most recent national polls.

But for all their differences, the latest polls agree on one thing - the Liberal Democrats have made progress in the past week. Both YouGov and ICM reported that support for Charles Kennedy's party was up two points on last week. On all the key issues more people say the Liberal Democrats have the best policy than a week ago.

The party is beginning to profit from the greater media exposure that it always secures in election campaigns, even if last week's coverage was not always friendly. However, ICM's polls in marginals indicate the party has yet to squeeze the Labour vote in those places where it hopes to make gains from the Tories. How far it does so will be vital to its prospects.

Labour still has to worry about fallout, if any, from the collapse of Rover. About that little is known - most polling was done before Friday's announcement.

John Curtice is professor of politics, Strathclyde University