The Conservatives are haemorrhaging support to Nigel Farage’s Brexit Party, new polling shows, with half of Tory voters ready to turn their backs on Theresa May.

Two separate surveys show the Tories’ vote share plunging since Mr Farage launched his new party last week, with one poll suggesting Labour would romp to victory if a general election was held now.

The Brexit Party is on course to top the polls in next month’s European Parliament elections, as Tories vent their “built-up anger and frustration” by switching their support to a party that better represents their views on Europe.

Labour, meanwhile, will lose hundreds of thousands of voters to Mr Farage if it continues to campaign for a post-Brexit customs union with the EU.

It is the latest evidence that voters now identify more strongly with Leave or Remain than they do with traditional political parties, and fuelled calls for Mrs May to quit.