Theresa May has insisted that cross-party talks are the best way to break the Brexit deadlock

Theresa May could face an unprecedented no-confidence vote among grassroots Tories, as the prospect of a crushing defeat in European elections looms.

Local party chairs have been circulating a petition that is on course to force the National Conservative Convention to hold an extraordinary general meeting where members could pressure the prime minister to resign.

The plot emerged as a poll showed Nigel Farage‘s new Brexit Party had stormed into the lead ahead of EU parliament elections next month.

A YouGov poll, commissioned by the People’s Vote campaign, puts the Brexit Party on 27 per cent, ahead of Labour on 22 per cent with the Conservatives trailing on 15 per cent.

It follows the burst of publicity the Brexit Party received with the launch last week of its election campaign, when it was announced that Annunziata Rees-Mogg – the sister of the leading Tory Brexiteer Jacob Rees-Mogg – would be among its candidates.

It will reinforce fears among ministers the Conservatives are heading for a crushing defeat if the poll on 23 May goes ahead as planned – a result which would almost certainly see fresh calls for Ms May to quit.

The prime minister has said she is determined to get a Brexit deal through Parliament before that date, which would mean voting would be cancelled.

However, that not only means winning a “meaningful vote” on a deal – which has already been rejected three times by the Commons – but also then passing a bill formally ratifying the agreement in law.

Much is likely to depend on whether cross-party talks with Labour can agree a common way forward – with the two sides expected to take stock of progress when MPs return to Westminster after the Easter recess.