Prime Minister David Cameron's Conservatives are on track to govern Britain for another five years even though they are likely to fall just short of an outright majority at Thursday's election, an exit poll showed.
The poll gave the Conservatives 316 of 650 seats in the lower house of parliament and the main opposition Labour Party 239. If accurate, that would be one of centre-left Labour's worst ever results.
Conservative government minister Michael Gove said that if the exit poll proved correct "the Conservatives have clearly won this election".
Such a result means Britain is likely to face a historic in-out European Union membership referendum in the next two years and that billions of pounds will be cut from government spending to eliminate the budget deficit in the world's fifth largest economy.
Sterling jumped to a one-week high after the poll. The pound jumped nearly US$0.02 to US$1.5430 in early Australasian trade, hitting its strongest since Apr 30.
UK election exit polls have a good track record but the large number of parties competing this time has raised the potential for error. It will be well into Friday before final results are announced.
The poll, conducted for Britain's national broadcasters, suggests Cameron will have multiple options to form a government, perhaps with the support of either the Liberal Democrats, his current coalition partners, or Northern Irish unionists or both. He could also try and go it alone.
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. Even if the centre-left party got together with the left-leaning Scottish nationalists and the Greens the exit poll suggested it would still be well short of the 326 seats needed for a majority in parliament.
Miliband, who was widely perceived to have performed better in the campaign than expected, would be likely to come under pressure to step down as leader.
The country's mostly right-wing press has long criticised him for being socially-awkward and presiding over what it has described as a dangerous lurch to the left.
Cameron has pledged to eliminate Britain's budget deficit, now running at five per cent of gross domestic product, by 2018/19, including through cuts to welfare spending of £12 billion (US$18.3 billion).