The anti-EU UK Independence Party (UKIP) looked set to take more seats in the European Parliament than any of the mainstream British parties as polls closed on Sunday.
Support for the UK Independence Party has been growing as British voters have become increasingly disillusioned with mainstream political parties, seen by many as failing to tackle immigration and an increasingly centralized European Union.
There are no exit polls for European elections in Britain, but as votes were being counted through the night UKIP were on target to win the election ahead of the Labour Party and the governing Conservatives.
UKIP's leader, Nigel Farage, called the results "an earthquake, because never before in the history of British politics has a party seen to be an insurgent party ever topped the polls in a national election."
Farage's party could take close to 30 percent of the total vote, up from 16.5 percent in the last European election in 2009.
"This demonstrates the deep-seated discontent with the political mainstream in Britain, as well as in the EU," Rob Ford, politics lecturer at Manchester University, told DW.
"A growing section of the British electorate feel threatened by immigration and social change, and left out of the political conversation," he said. "Anti-EU sentiment is part of this, but only a small part - domestic political disaffection is more important."
Prime Minister David Cameron's Conservative Party has long been bleeding supporters to UKIP. To assuage both voters and backbenchers in his own party, Cameron has promised a referendum on EU membership by 2017 should the Conservatives win a majority in next year's parliamentary elections.
No Front National deal
The UKIP win reflected strong support elsewhere in Europe for anti-EU parties, notably the Front National in France. But UKIP on Sunday reiterated their refusal to cooperate in the European Parliament with the FN, which they see as being too far-right and racist.
"UKIP has invested a considerable amount of effort in trying to say they're not racist, they're not xenophobic - they're merely critical of the European Union," said Andy Mycock, political scientist at the Huddersfield University. "The problem is most of the stories that have come out during the latest election cycle have actually highlighted that some members of UKIP standing for election have racist views."
Several UKIP members have been excluded from the party in the past year after expressing views which the leadership said was unacceptable.
A much stronger UKIP in the European Parliament will not have much impact on the workings of the chamber, but analysts say the strong support for the party will redefine politics at home.
"It's clear that UKIP are tapping into a general frustration in the United Kingdom with the political elite," Mycock said. "At the moment, none of the other parties are particularly sure about their attitudes towards Europe, and in many ways UKIP is offering a firmer policy framework than the other parties - and that may be why people are voting for them."
Since being founded in 1993, UKIP has largely been a one-issue party, working to get Britain out of the EU. Until Sunday night the party held nine of Britain's 73 seats in the European Parliament, but it has no members in the British parliament in London.
In recent years UKIP has been preparing a broader platform, aiming to become a real force in national politics too. The party made considerable gains in local elections last week. Yet many voters still believe UKIP is too far away from establishing themselves as a proper political alternative to Britain's three main political parties - the Conservatives, Labour, and the Liberal Democrats.
"Farage seems to be able to connect with both working and middle classes," said Neil Drogie, a Conservative voter in Manchester. "But as a ruling party what ideas would they really have? It's easy to say 'get out of Europe, curb immigration' and so on, and it's what a lot of people want to hear. But no one from UKIP has explained their vision for our country if we did leave the EU."
Voter turnout for the EU elections in the UK was 36 percent, two percent higher than in 2009, but lower than the EU average this year, at 43.1 percent.