The Conservatives are facing a humiliating defeat at the European elections next month after support for the party slumped to its lowest level since 2013, according to a new poll.

The survey shows the Tories on just 28 per cent when it comes to general election voting intention – a four-point fall which leaves them trailing Labour on 32.

When voters were asked which party they will vote for at the European elections, Theresa May’s party languished on 16 per cent, eight points behind Labour on 24.

In a clear sign support for the Conservatives is crumbling over the failure to deliver Brexit, 56 per cent of people who voted to leave at the 2016 referendum said they would back Ukip or Nigel Farage’s newly formed Brexit Party during next month’s vote.

The Brexit Party is on 15 per cent, while Ukip stands at 14 per cent when it comes to European voting intention, the YouGov poll for The Times indicated.

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By comparison, the Lib Dems and the Greens are both on 8 per cent, while Change UK has 7 per cent support.

No 10 is still hoping to get a deal through parliament in time to avoid participation in the European elections on 23 May. But the UK is formally on track to hold the poll, having informed the EU authorities ahead of Friday’s deadline that it would be taking part.

Boris Johnson’s backers have suggested he may not even campaign on behalf of his party next month in an effort to show his displeasure at the UK’s involvement.

“Boris won’t campaign in European elections. He believes the prospect of the UK fielding candidates is utterly preposterous,” a source told The Times.

Last week Nadhim Zahawi, the children’s minister, said taking part in the May elections would be the Conservatives “suicide note”, suggesting the level of anger expressed during the vote would be an “existential threat” to his party.

Last night Philip Hammond, the chancellor, admitted the European elections “feels like a pointless exercise” and also acknowledged senior figures were “jockeying for position” to succeed the prime minister.

Yet he insisted Ms May would stay on until she has taken Britain out of the EU.

He told Bloomberg: “The prime minister has said that she will leave once she has done the deal and taken us out of the European Union. But, as far as I know, she doesn’t have any intention of leaving until that deal is done.”

The latest YouGov poll shows Ms May’s personal ratings remain largely unchanged.