Nigel Farage’s Brexit party is on course to secure more support at the European elections than the Tories and Labour combined, according to the latest Opinium poll for the Observer.

In the most striking sign to date of surging support for Farage, the poll suggests more than a third of voters will back him on 23 May. It puts his party on 34% of the vote, with less than a fortnight before the election takes place.

The poll suggests support for the Conservatives has collapsed amid the Brexit uncertainty, with Theresa May’s party on just 11%. Labour is a distant second, on 21%. The Lib Dems perform the best of any of the openly anti-Brexit parties, one point ahead of the Tories on 12% of the vote.

With the Brexit party securing more than three times the level of support for the Tories, the poll confirms the concerns of senior Conservatives that it is haemorrhaging support as Brexit remains unresolved. Just a fortnight ago, the Brexit party was neck-and-neck with Labour on 28%. Now it has a 13-point lead over Jeremy Corbyn’s party.

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The Conservatives are now only narrowly ahead of the Brexit party when voters are asked who they would vote for at a general election. The Tories are on 22% support, down 4% on a fortnight ago, with the Brexit party on 21% backing. Labour leads on 28%, but is down five points on the last poll.

Leave voters seem to be flocking to the Brexit party. A fortnight ago, it was joint first with the Conservatives among leave voters in terms of general election voting, with both on 33%. It now appears to be the clearer choice of leave voters, with 40% saying they will vote for the Brexit party and 27% backing the Conservatives.

May is also close to losing her lead over Corbyn as to who voters regard as the best prime minister. Her lead has dropped from four points to just one point.

The Opinium poll also found that despite the dominance of Brexit as an issue since the 2016 referendum, there was a significant proportion of voters who did not know each party’s position on it. The poll reveals 36% are not aware of the Conservative party’s stance, while 38% say the same about Labour.

For those who said they knew, 23% think the Conservatives support a soft Brexit, while 23% think they support a hard Brexit. For the Labour party, 25% think they support remaining in the EU, while 31% think they support a soft Brexit.

Opinium polled 2,004 people online between 8-10 May.