Britain's eurosceptic UK Independence Party made strong gains but its Dutch counterparts stumbled in European parliament elections expected to produce a widespread anti-EU vote thanks in part to a low turnout.
Nigel Farage's UKIP, which wants to pull Britain out of the European Union and severely restrict immigration, grabbed seats from the governing Conservatives and the opposition Labour Party in local elections held at the same time as the EU vote, partial results showed.
If those scores are confirmed or amplified in the European ballot, results of which will be released late tomorrow, it could increase pressure on Conservative Prime Minister David Cameron to take a harder line on reducing the EU's powers.
"Looking at the average vote shares across the country, and without wishing to count any chickens before they're hatched, it looks pretty good," an ebullient Farage said.
"They'll say it's a protest," Farage said in Thurrock, Essex, a Labour target where voters turned to his party. "It looks like a fairly permanent protest."
The question faced by the leaders of all three of Britain's main parties - Labour leader Ed Miliband, Liberal Democrat Deputy Prime Minister Nick Clegg as well as Cameron - is how to win back voters who have switched to UKIP.
"The immigration floodgate needs shutting - how can you bring more people over if there's not enough jobs for your own people?" James Donaghy, 66, said as he voted for UKIP in Sevenoaks, southeast England.
Farage, who may opt to contest a seat in Kent in the general election, said the results provided a springboard for his party as it prepared for next year's vote.
By contrast, far right Dutch populist Geert Wilders, whose anti-EU, anti-Islam Freedom Party had been forecast to top the poll in the Netherlands, was beaten into fourth place by pro-European parties in a surprise reverse.
Wilders blamed the disappointing score on a low turnout of 35 per cent, saying that "by staying home voters showed their loathing for and disinterest in the European Union. The Netherlands has not become more pro-European."
Voters in Ireland and the Czech Republic were casting their ballots yesterday, but most of the EU's 28 nations hold the election tomorrow. About 388 million Europeans are eligible to vote for 751 members of the parliament, which is an equal co-legislator with member governments on most EU laws.
Opinion polls suggest anti-EU parties of the far right and hard left, which blame Brussels for austerity and unemployment in the wake of the euro zone crisis, may win about 25 per cent of seats, roughly double their present share.
But the parliament will remain dominated by pro-European centre-right, centre-left, liberal and Greens parties that often vote together in support of EU legislation.
In France, final polls put Marine Le Pen's far right National Front, which wants to leave the euro and restore border controls and trade barriers, neck-and-neck with the conservative UMP party ahead of tomorrow's vote, with President Francois Hollande's Socialists a distant third.
Other countries where Eurosceptics are expected to do well include Italy, Austria and Denmark.
Additional reporting by Bloomberg