But analysis of recent polls suggests that the cut in the Labour lead from 23 to 14 points, in NOP polls two weeks apart, is unlikely to be borne out in other polls over the next few weeks.
Conservative strategists argued that the poll was a "turning point" which reflected economic good news finally feeding into Tory popularity.
But Professor David Sanders of Essex University said it was "much too early" to say whether this was the case. He said that the usual indicators of economic well-being had ceased to predict levels of Tory support when Britain was forced out of the European exchange rate mechanism in September 1992.
Over the past year, despite low inflation, falling unemployment and big tax cuts, Tory support has been drifting only slowly upwards.
Chris Patten, the Tory chairman who ran the 1992 election campaign, responded cautiously to the poll, describing the question of whether the Tories could restore the "umbilical link" between economic and political recovery as the "key ingredient".
Now the Governor of Hong Kong, Mr Patten said on BBC Television: "If I was either Tony Blair or John Major that would be the issue that would most interest me."
Professor Sanders - whose computer forecast of the last election was accurate within 0.2 per cent - says that, since the exchange rate mechanism debacle, there has still been a close relationship between people's perceptions of the economy and their voting intentions. And the evidence is that the electorate's perceptions are not changing dramatically. In particular, according to Professor Sanders, the Tories need more people to think they would be better than Labour at handling economic difficulties.
On Gallup's latest figures, Labour's lead on this question widened from 16 points to 21 points at the beginning of this month. It needs to be turned into a Tory lead of more than 6 points if John Major is to stay in Downing Street, Professor Sanders says.
The second requirement for a Tory win is that more voters have to become confident their family will be better off over the next year - the traditional measure of the "feelgood" factor. Again Gallup's most recent figures have moved in the wrong direction for the Government.
Even to forecast a hung parliament requires "heroic" assumptions about a transformation in the electorate's views, Professor Sanders said.
The NOP poll for yesterday's Sunday Times - taken last Thursday - put Labour on 47 per cent, the Tories on 33 per cent and the Liberal Democrats on 14 per cent.
This marked a sharp change from a poll taken, again on a single day, two days after Mr Blair's conference speech. But it was not so out of line with the previous NOP poll, which gave Labour a 19-point lead in mid-September.
A Gallup poll taken before and after Mr Blair's speech showed a similar "bounce", with the Labour lead widening by 8.5 points.
If yesterday's NOP poll shows anything, it suggests this was a temporary phenomenon.Reuse content