Updated at 1.25pm

Voters in Brexit-bound Britain cast ballots Thursday at the start of 28-nation EU elections in which eurosceptic, anti-immigration forces have vowed to create a political earthquake that will shake the Brussels establishment.

With Prime Minister Theresa May's resignation appearing imminent after she postponed a forlorn attempt to push her divorce deal through parliament, Britain joined the Netherlands in kicking off four days of voting across the continent.

The elections were a surreal spectacle for a country that voted almost three years ago to leave the European Union, with May vowing on countless occasions to honour the result in time to avoid the election.

The Brexit crisis mirrored deep divisions across the continent.

Rising anti-establishment forces across the continent are bidding to make significant gains, in a threat to closer EU integration.

More than 400 million European voters are eligible to elect 751 Members of the European Parliament, with the first results announced late Sunday once voting in all 28 member states has been completed.

These are the ninth European parliament elections since they began in 1979 and voter turnout has dropped each time, hitting 43 percent in 2014.

'Peaceful political revolution'

Having opted to leave the EU in a seismic referendum in 2016, Britain was originally meant to depart on March 29 and therefore not take part in the contests.

But MPs have rejected May's withdrawal agreement and the country now finds itself in the absurd situation of electing lawmakers to an institution it plans to leave.

The issue looked set to dominate how Britons vote.

"Once you've made a decision to leave I felt that we should have executed it," said Neil Rodford, 49, as he cast his ballot in southwest London.

Accountant Margaret Clark, 64, felt the opposite as she voted in Northern Ireland.

"What's mostly on my mind is the fact that I would like to remain in the European Union," she told AFP.

The Brexit Party, formed only this year by eurosceptic figurehead Nigel Farage, is leading the latest opinion polls with 37% of the vote.

Amid widespread frustration at the political gridlock, the ruling Conservatives are in fifth place with just seven percent while the Labour opposition also lag behind on 13.

"We are attempting a peaceful political revolution in this country," Farage told the party's final rally this week.

"The establishment: they're not frightened - they're absolutely terrified!" he said of his new party's rise.

Opposed to closer EU integration

Around the continent, national leaders are scrambling to mobilise their supporters to resist the populist surge, with opinion polls showing nationalist parties in the lead in France, Italy and Hungary, among others.

Pro-European leaders fear a good showing for the eurosceptics will disrupt Brussels decision-making, threatening reform efforts at closer integration.

In the Netherlands, flamboyant populist Thierry Baudet, a classics-quoting climate sceptic, is on course to win the same number of seats as Prime Minister Mark Rutte's Liberals.

Once best known for naked Instagram selfies and controversial comments about women, Baudet, 36, stunned Europe in March when his Forum for Democracy became the biggest party in the Dutch senate.

Matteo Salvini of Italy's anti-immigrant League and Marine Le Pen of France's far-right National Rally (RN) want their Europe of Nations and Freedom (ENF) group to become the third largest in Brussels. The League has topped opinion polls in Italy.

Meanwhile Le Pen wants to strike a blow to Emmanuel Macron's faltering French presidency by overtaking his centrist, pro-European party Republic on the Move.

Polls give her RN party a slight edge, with around 23 percent support.

"Everything has changed," Le Pen told AFP.

"In the space of a few months, a whole range of political forces have risen up in spectacular fashion."

Centre-right set to win

However, the strong showing by eurosceptics is not expected to sweep the whole bloc, with voters from Spain to Ireland and the former Soviet Baltic states indicating solid backing for the EU.

In Germany, surveys show Chancellor Angela Merkel's CDU party - a heavyweight in the EU-wide centre-right EPP group - in first place, with the Greens second.

The latest Eurobarometer survey commissioned by the European Parliament found 61% of respondents calling their country's EU membership a good thing - the highest level since the early 1990s.

The polls will open on Friday in the Czech Republic and Ireland, and on Saturday in Latvia, Malta and Slovakia.

But most countries will be voting on Sunday, with the results expected overnight into Monday.

Nine different projections this month gave the EPP the most seats ahead of the main centre-left PES bloc and then the ALDE liberals.

Former Luxembourg prime minister Jean-Claude Juncker is stepping down after five years as president of the European Commission.

EPP leader Manfred Weber is their candidate to replace him, while the PES is putting up former Dutch foreign minister Frans Timmermans.

The hunt will also be on for someone to replace former Polish premier Donald Tusk as head of the EU leaders' council.

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