LONDON, May 8 (Reuters) - Britain's voters have delivered a painful blow not just to the Labor Party but also to the opinion pollsters, who had suggested a very different outcome to Thursday's election.
With votes counted in almost all of the 650 constituencies, the Conservatives were on course for an overall majority of over 326 seats in the House of Commons with Labor doomed to languish on the opposition benches with almost 100 fewer seats.
The result came as a complete shock to everyone after polls had been suggesting for months that the two big parties were neck-and-neck and neither of them would come close to winning an overall majority.
"There's only one opinion poll that counts and that's the one on election day and I'm not sure that's never been truer than it is today," Prime Minister David Cameron said after winning his own seat, Witney.
Some pollsters admitted something had gone badly wrong, and they did not yet understand what.
"Election results raise serious issues for all pollsters. We will look at our methods and have urged the British Polling Council to set up a review," said Populus, one of the main polling firms, on Twitter.
Others, such as Survation and ComRes, defended their work, pointing out they had been right about the surge of the Scottish National Party, the collapse of the Liberal Democrats and a sharp increase in vote share for anti-EU party UKIP.
Andrew Hawkins, chairman of ComRes, said this fragmentation of the political landscape had presented pollsters with "extra headaches" by turning the election into a "patchwork of regional contests" where national trends were less relevant.
The polls had converged to suggest the Conservatives and Labor were tied or within a point or two of each other on about 32 or 33 percent of the vote share. In fact, the Conservatives won about 37 percent while Labor won about 31 percent.
RETURN OF THE SHY TORIES?
Rob Ford, one of Britain's most respected political scientists, drew comparisons with the polling disaster of 1992, when Labor were expected to win but the Conservatives beat their polling average by 9 points to romp home.
"Pollsters always mutter the words 1992 in a kind of horrified tone. They can now add 2015 to the recollections of horror," he told Reuters.
The problem in 1992 was identified as the so-called "shy Tories" who were reluctant to own up that they would vote Conservative at a time when the party was perceived to be unpopular. Tory is another name for Conservative.
But Ford said while there may have been some shy Tories this time, that was at best a partial explanation as pollsters had all been adjusting their data to reflect that known phenomenon.
Another possibility was that pollsters had not captured representative samples of the electorate, and only experimentation with methods would address that in future.
"Polls, in the UK and in other places around the world, appear to be getting worse as it becomes more challenging to contact a representative sample of voters," said U.S. forecasting guru Nate Silver on his FiveThirtyEight website.
It was also possible that voters who were undecided until the last minute had overwhelmingly voted Conservative, making their minds up too late for the polls, said Ford.
Questions were also being raised about why different polls had converged towards similar findings that were all wrong.
"These were different pollsters with different methodologies but everyone missed this. It's a very, very big miss and at this stage we just don't know why. We're shocked," said Ford.
Damian Lyons Lowe, chief executive of Survation, said he had "chickened out" of publishing an eve of election poll that gave results much closer to what came to pass because it seemed such an outlier, suggesting that some data had perhaps been ignored.
Further complicating the picture, under Britain's first-past-the-post electoral system, what matters is coming first in individual seats rather than the national share of the vote.
That meant Labor lost over 20 seats despite increasing its share of the vote by about two percentage points since 2010, while the Conservatives gained over 20 seats despite increasing their vote share by less than one percentage point.
The main problem for Labor was that it was wiped out in Scotland, losing 40 seats there to the Scottish National Party.
Labor also failed to take key swing seats from the Tories in parts of England such as the East Midlands, and although its support increased in other regions such as Yorkshire, that merely increased its majorities in seats it already held there.
"Labor's problems have turned out to be even worse than the national swings imply ... because it's gaining votes in areas where it doesn't help them while losing votes in places where it hurts," said Silver. (Editing by Giles Elgood)