Tom Simpson, managing director of Harris Research, has estimated what might happen if people behave the way they did at the last election, and suggests Labour's lead in the real vote today could be cut to 11 points.
Although all the polls, apart from MORI, adjust the don't knows and won't says to take account of Conservative supporters who are reluctant to declare themselves, Mr Simpson said: "We can't be sure we've got all of them this way, so we've made a stronger adjustment on the basis of what happened last time."
He assumes a late swing on the same scale as in 1992. Applying this adjustment to today's poll cuts Mr Blair's majority of 173-179 seats to around 99.
But the evidence from the poll itself suggests that Labour's vote is solid. While 81 per cent of Labour supporters said they had "definitely decided" how to vote, only 68 per cent of Tory voters were sure.
Of Tories, 23 per cent said: "I may change my mind", against 33 per cent of Liberal Democrats and only 13 per cent of Labour supporters. The second preferences of Tory waverers tilt towards the Liberal Democrats, while those of Liberal Democrats split nearly three-to-one in Labour's favour.
We asked which party voters trusted most to take the right decisions in five areas and found Labour ahead in each one.
On the economy, income tax and prices (see table), our questions are directly comparable with those asked by NOP in the BBC's exit poll at the last election. Labour's rating is 13 or 14 points higher than in 1992, and the Tories are between 14 and 18 points lower.
Labour was also ahead by 16 points on law and order and by 12 points on Europe. When Harris asked about the impact of the European Union as an election issue, 24 per cent said it made people less likely to vote Conservative, against 16 per cent who said it made people more likely to do so.
Harris also asked: "What is the one most important reason for supporting the party you intend to vote for?"
This is comparable to a question Harris asked in its exit poll for ITN in 1992, and the answers are very similar. "The party's policies" were named by 45 per cent (47 per cent in 1992); "I usually vote for that party," 20 per cent (20); "Dislike of another party," 15 per cent (15); "The party leader" , 7 per cent (7); "The local candidate" 4 per cent (5).
Finally, Harris asked what people thought of the "new" Labour Party. Half the sample, 49 per cent, said the changes show Tony Blair "is a strong leader with a clear sense of direction". Of Conservative voters, 23 per cent also thought that Mr Blair was a strong leader.
Harris Research interviewed 1,154 adults face-to-face in their homes on Sunday, Monday and Tuesday this week. The figures exclude 14 per cent who didn't know, wouldn't say or wouldn't vote, who could not be allocated to a party on the basis of how they voted in 1992.
Which party do you trust most to take the right decisions
about ...? (1992 NOP/BBC exit poll in brackets)
The economy Income tax Prices and
Labour 49 (35) 45 (32) 46 (33)
Conservative 34 (51) 35 (53) 39 (53)
Lib Dem 10 (14) 15 (15) 10 (14)Reuse content