Prime Minister David Cameron's Conservatives are set to govern Britain for another five years after an unexpectedly strong showing, but may have to grapple with renewed calls for Scottish independence after nationalists surged.
Ed Miliband, leader of the main opposition Labour Party, all but conceded defeat on Friday morning, saying he was "deeply sorry" for a "very disappointing and difficult night."
Cameron said he hoped to form a government in the coming days after his party enjoyed what he described as a "very strong night."
With nearly three quarters of seats counted, the Conservatives had won 203 of 650 seats with an exit poll suggesting they were on track to win 316 seats in the lower house of parliament, just shy of a majority but with ample options to form a government.
Some pollsters said an overall Conservative majority could not be ruled out and the latest BBC projection suggested Cameron's party could win as many as 325 seats.
In practice, controlling 323 seats in parliament is enough to command a majority as four lawmakers from Northern Ireland's Sinn Fein refuse to take their places.
In Scotland, once a Labour stronghold, the Scottish National Party (SNP) appeared to have won almost every seat, a result likely to stoke momentum for Scottish independence by underscoring the political chasm that divides voters north of the border and the rest of the United Kingdom.
A Conservative victory means Britain is likely to face a historic in-out European Union referendum within two years, something Cameron has promised to deliver if re-elected.
Professor Vernon Bogdanor, a constitutional expert, said Cameron would be the first premier to gain seats since Margaret Thatcher in 1983.
For Labour, the election represents a crushing defeat.
Exit polls forecast it would get just 239 seats. If accurate, that would be the center-left party's worst result in almost three decades. The scale of its defeat in Scotland at the hands of nationalists is likely to raise serious questions about its future direction and policies.
If Cameron falls just short of an outright majority it looks like he will have multiple options to form a government anyway, perhaps with the support of the Liberal Democrats, his current coalition partners, or Northern Irish unionists or both.
He could also try and go it alone.
With all of Scotland's 59 parliamentary seats counted, the SNP won 56 of them, all but obliterating Labour north of the border.
That was a gain of 50 seats over the nationalists' previous six seats in the 650-seat House of Commons.
The opposition Labour Party lost 40 seats in Scotland. The result left the Conservatives, Labour and the Liberal Democrats with just one seat each in Scotland.
Opponents fear the SNP is preparing to use the win to renew its push for an independence referendum even though it lost such a plebiscite only last year.
"We're seeing an electoral tsunami on a gigantic scale," said Alex Salmond, the party's former leader.
"The SNP are going to be impossible to ignore and very difficult to stop," he said, saying such a result would strip Cameron of any legitimacy in Scotland where his Conservative Party would have only one lawmaker.
Early on Friday Cameron said that he wanted to implement plans for further devolution of political powers to Scotland and Wales as fast as possible.
In a blow to Labour, Douglas Alexander, the party's campaign chief and foreign policy spokesman, lost his seat to a 20-year-old student while Scottish Labour leader Jim Murphy was lost.
The centrist Liberal Democrats, who have governed in coalition with the Conservatives for the past five years, suffered stinging losses with the exit poll predicting they would finish with just 10 seats across the United Kingdom.
That would be a disaster for leader and deputy prime minister Nick Clegg, who called it a "cruel and punishing" night.
The UK Independence Party, which wants an immediate British withdrawal from the European Union, was on track to get two seats at best amid speculation that Nigel Farage, its leader, would fail to be elected and therefore have to step down.
Labour leader Miliband, who was widely perceived to have performed better in the campaign than expected, is likely to come under pressure to step down in the coming hours.
Indeed if the exit poll is right, three of Britain's political parties could soon be looking for a new leader.