Sunday's election was held against the backdrop of political disarray in Britain that saw PM Theresa May announce her resignation after failing to deliver Brexit on time
Anti-EU populist Nigel Farage's Brexit Party triumphed early Monday in European Parliament elections that Britain was never meant to hold, while the ruling Conservatives suffered a historic blow.
But the polls exposed the divisions that remain three years after Britons voted to leave the European Union, with the pro-EU Liberal Democrats and Greens also making huge gains.
Sunday's election was held against the backdrop of political disarray in Britain that saw Prime Minister Theresa May last week announce her resignation after failing to deliver Brexit on time.
Farage only registered his party in February but with most results declared, it won 28 out of 73 available seats with almost 32 percent of the vote.
Much of this support was at the expense of May's Conservative party, which slumped to nine percent of the vote, apparently its worst electoral performance since 1832.
But the main opposition Labour party, which has been accused of a confusing position on Brexit, also took a hit with its vote share falling to around 14 percent.
Farage, the lead campaigner in the 2016 referendum to leave the EU, said his party should now have a say in any new Brexit negotiations with Brussels.
And he warned that failure to leave the EU on October 31 -- the latest Brexit deadline -- would see his party replicate its victory in a general election.
"We are getting ready for it," he warned in Southampton as ballots were being counted in his South East region.
However, he acknowledged the result reflected a split in nationwide opinion similar to that expressed when Britons voted by 52 to 48 percent to leave the EU.
The Liberal Democrats, who want another referendum with the goal of reversing Brexit, came second with around 20 percent of the vote and 15 MEPs, while the similarly pro-European Greens were on 12 percent.
Britain had planned to leave the EU on March 29 and these European elections were never meant to happen, but parliament's inability to agree on how to leave has left the country in limbo.
Farage said his party won with "a big, simple message, which is we've been badly let down by two parties who have broken their promises".
May's bickering Conservative party -- now in the throes of a leadership contest involving much of her current cabinet -- had been braced for poor results and barely bothered to campaign.
But Foreign Secretary Jeremy Hunt said there was an "existential risk to our party unless we now come together and get Brexit done".
The result for Labour meanwhile triggered a fresh bout of arguing within the party over its strategy, which backs Brexit but holds open the option of a new vote.
"This issue will have to go back to the people, whether through a general election or a public vote," Labour leader Jeremy Corbyn said afterwards.
Several of his close allies went further, however, including his finance spokesman John McDonnell, who said the party "can't hide from hit we took last night.
"Now we face prospect of Brexiteer extremist as Tory leader & threat of no deal, we must unite our party & country by taking issue back to people in a public vote," he said on Twitter.
The Conservatives must now decide what they intend to do about the long-suffering EU withdrawal deal May reached with Brussels last year.
Parliament has rejected the pact, intended to smooth Britain's exit, three times and was on course to do so again before May announced she would quit.
The EU refuses to re-open the deal, and Conservative leadership favourites such as Boris Johnson have raised the prospect of leaving with no agreement in October.
"No one sensible would aim exclusively for a no-deal outcome," Johnson wrote in Monday's Daily Telegraph, but added: "No one responsible would take no-deal off the table."
Some analysts think the results from the European elections will force the other UK leadership hopefuls to adopt the same tough line.
"Any swing away from the Conservative Party is being interpreted by pretty much all the party leadership candidates as a push toward a harder, serious, no-deal Brexit," University of Bedfordshire professor Stephen Barber told AFP.
However, parliament has voted repeatedly against a "no deal" Brexit, fearing the economic impact.
And May's Finance Minister Philip Hammond warned on Sunday he might even be prepared to take the drastic step of voting to bring down a future Conservative government in order to avoid this situation.