This article appeared in The Independent, Wednesday 30 April 1997 and is reprinted with their kind permission.
The atmosphere in one polling company's office was described as "frantic" yesterday as pollsters prepared to publish their final figures tomorrow - the ones on which they will be judged. After the disaster of 1992, when the opinion polls mis-estimated the Tory lead by between seven and 11 percentage points, their reputation is on the line.
Harris for The Independent will publish its final poll, based on interviews carried out on Sunday, Monday and yesterday.
ICM, which last week lifted Tory hopes with a poll putting them only five points behind Labour, will be closely watched in tomorrow's Guardian.
Gallup's daily poll for the Telegraph, which today suggests hardly any movement in opinion will roll to its conclusion.
A separate Gallup poll for Channel 4 News last night showed Labour's lead down one point at 18 points. NOP produces its last gasp for Reuter (sic) news agency this morning.
MORI will produce a final poll for the Times with a double-sized sample of over 2,000 interviews carried out yesterday, followed by a late poll for the London Evening Standard for which 1,000 interviews will be carried out tonight.
Tomorrow night, two polling companies will put their reputations at additional risk by carrying out exit polls.
NOP and MORI will stop 15,000 people each on their way out of 300 polling stations on behalf of the BBC and ITN respectively. The results of both polls will be announced simultaneously at 10 pm, when voting booths close.
The BBC has decided not to use its exit poll to forecast he number of seats each party will win, after going on air in 1992 with the prediction that John Major would be "short of an overall majority by 25 seats".
ITN, on the other hand, will boldly declare the size of the majority its exit poll suggests for Tony Blair (or Mr Major).
Today, the average of the penultimate polls from each of the main polling companies puts the Labour Party on 47 per cent, 16 points in front of the Conservatives on 31 per cent, with the Liberal Democrats on 15 per cent.
This represents a 12-point swing from Tory to Labour since the last election, and, if such a swing were uniform across the country, would produce a Commons majority for Mr Blair of around 150 seats, a landslide comparable to the 144-seat majority won by Margaret Thatcher in 1983.
The pollsters believe they have dealt with some of the sources of their error five years ago, by updating their profile of the electorate and adjusting for "reluctant Tories".
About a quarter of the error last time was due to pollsters assuming voters were more working-class than they were. Some of the remaining difference was down to Tory voters being unwilling to take part in polls.
All the companies, apart from MORI, now allocate some of the "don't know"s and "won't say"s to the party they say they voted for at the last election.
One factor which cannot be picked up except by polling as late as possible, is late swing. At the last election an unknown number of voters changed their minds at the last minute.