John Curtice: Labour slides in polls as Darling works his magic

Alistair Darling has apparently worked his electoral magic once again. When the Chancellor delivered his pre-Budget report last October Labour's average poll rating, already on the slide, fell by a further two points. When Mr Darling told an astonished House of Commons that the Revenue and Customs had lost the financial details of everyone in receipt of child benefit, his party's poll ratings fell by five points.

Now, two polls conducted in the immediate wake of the Chancellor's first Budget statement suggest Labour's support has fallen by five points, from an average of 34 per cent in five polls conducted just before the Budget to just 29 per cent now.

One of the two new polls, undertaken by YouGov, puts Labour on just 27 per cent, no less than 16 points behind the Conservatives. Although misleadingly reported as Labour's worst poll rating since 1983 – two polls undertaken for this newspaper over the past 12 months also put Labour on 27 per cent – it is the biggest Tory lead recorded in any poll for more than 20 years.

On its own one such poll could be dismissed as a "rogue". Statistical theory tells us that even a well-conducted poll will under- or overestimate a party's true standing by more than three points one time in 20. Just occasionally the error will be even bigger. Perhaps, it is YouGov's misfortune to have suffered such a fate.

It is this possibility that makes the second poll, conducted by ICM, so important. This shows a much smaller Tory lead – nine points. Nevertheless, that is still six points up on ICM's previous poll. YouGov may have exaggerated Labour's loss of support, but the chances are very low indeed that two polls would show a decisive drop in Labour support if the tide of public opinion had not turned against the party at all.

Ironically, many of the individual measures in the Budget appear to be relatively popular, not least the increase in taxation on gas- guzzling cars and charging for plastic bags. However, the whole seems to be regarded less favourably than the sum of its parts; nearly one in three believe the Budget will make things worse while only 7 per cent think it will improve them. Meanwhile nearly half think that Mr Darling is not up his job. Mr Darling's problem may be an inability to lift morale.

Doubtless these latest polls will help quell some of the unease in the Conservative Party about its apparent lack of electoral pro-gress. However, every post-war opposition that won the next election secured 50 per cent in the polls at some point. Mr Cameron is a long way from that target.

John Curtice is professor of politics at Strathclyde University