Nigel Farage's anti-EU Brexit party topped European Parliament polls in Britain, putting intense pressure on the ruling Conservatives who suffered a historic rout and raising the chances of a no-deal outcome.
The populist party, founded just three months ago, capitalised on public anger over delays to Britain's exit from the European Union, winning nearly 32 percent with almost all votes counted on Monday.
Prime Minister Theresa May's Conservative party meanwhile slumped to nine percent, its worst electoral result since 1832.
In a sign of the divisions still gripping Britain three years after the referendum vote for Brexit, the pro-European Liberal Democrats and Greens also made significant gains.
The elections, which took place on Thursday, were never meant to happen, as Britain was due to be out of the bloc on March 29.
But parliament has been unable to agree on how to leave, slowly sapping May's authority and forcing her to finally announce last week she would quit to let somebody else try.
Describing the result as a "very disappointing night", she said: "It shows the importance of finding a Brexit deal, and I sincerely hope these results focus minds in parliament."
Several of those vying to replace her, including Boris Johnson, were quick to repeat that Brexit must happen by the latest deadline, October 31, with or without a deal with Brussels.
"We can and must deliver. No one sensible would aim exclusively for a no-deal outcome. No one responsible would take no-deal off the table," Johnson wrote in Monday's Daily Telegraph.
It was also a bad night for the main opposition Labour party, which has been accused of a confusing position on Brexit and slumped to 14 percent.
Eyeing the success of the Liberal Democrats and Greens, who want a second referendum to reverse the whole process, senior Labour figures said it was time for their party to decisively back another vote.
Boris Johnson. The PM contender will face allegations he lied in the run up to the EU referendum over how much the UK sent the EU each week. Source: AP
'Stun everybody'
Farage only registered the Brexit Party in February but built on his support as a leading campaigner in the 2016 referendum, when he led the now largely defunct UK Independence Party (UKIP).
"If we don't leave on October 31, then the Brexit Party will go on to a general election and stun everybody there too," Farage told reporters in London on Monday.
He said his party should now have a say in any new Brexit negotiations with Brussels.
The EU has said it will not re-open the withdrawal deal already agreed with May, but many of her would-be successors are still likely to try.
Brexit Party leader Nigel Farage with the Brexit party MEPs during a post election press conference Source: AP
'Almost certainly' a referendum
Anti-Brexit campaigners also hailed the success of parties who want to keep Britain in the EU, suggesting voters are as split as they were when they voted 52 to 48 percent to leave in 2016.
The Liberal Democrats came second with around 20 percent and 16 MEPs, up from just one MEP in the last European elections in 2014.
The Greens, who campaigned on an anti-Brexit ticket as well as for action on climate change, won seven seats with 12 percent of the vote.
Adding in votes for the Scottish National Party and Plaid Cymru in Wales, both of which want a second referendum, supporters saw a resounding victory for pro-EU forces.
"There will almost certainly be a referendum now and we've got to win that," Lib Dem leader Vince Cable told AFP at an event with the party's new MEPs on Monday.
Analysts, however, warned that European election results cannot be easily translated into success at British parliamentary elections, not least because a different voting system is used.
May's bickering Conservative party had been braced for poor results and barely bothered to campaign.
