An electoral worker empties a ballot box after polls closed in Britain's general election at a counting centre in Doncaster, May 7, 2015. [Photo/Agencies]

STUNNING SCOTTISH FORECAST

The same poll said the Scottish National Party (SNP) would win 58 of Scotland's 59 seats, all but wiping Labour out in its former stronghold.

Opponents fear the SNP is preparing to use an emphatic win to renew its push for an independence referendum even though it lost such a plebiscite only last year.

SNP leader Nicola Sturgeon said the exit poll's prediction should be treated with huge caution. But even if the final tally is a little lower it would still be the nationalists' best result in a UK-wide election by a huge margin.

The centrist Liberal Democrats, who have governed in coalition with the Conservatives for the past five years, will finish with just 10 seats, the exit poll said. If confirmed, that would represent a disaster for leader and deputy prime minister Nick Clegg.

The UK Independence Party, which wants an immediate British withdrawal from the EU and enjoyed a poll surge last year, was on track to get just two seats.

A separate poll of Britons who had already voted by YouGov extrapolated a more even result however, putting the Conservatives on 284 seats and Labour on 263, the Liberal Democrats on 31 and the Scottish Nationalists on 48.

Before the election, opinion polls had shown the Conservatives and Labour neck-and-neck, leaving that industry facing a potential inquest.

If the main exit poll is accurate, Cameron's position as Conservative leader, which had been looking shaky before the election, would be secure. By exceeding expectations he could expect to quell dissent within his party.

Conversely, the result would be a crushing defeat for Labour and Ed Miliband, its leader.