A leading Conservative donor is threatening to fund a new pro-Brexit party if Theresa May fails to deliver on the EU referendum.

Jeremy Hosking, a City financier who donated £1.5 million to the Leave campaign and has given £375,000 to the Conservatives since 2015, has carried out private polling he believes shows “clear support” for a new party that would help achieve “what the electorate thought it would be getting” following the 2016 vote.

Mr Hosking, who says Leave voters are “being heated up slowly like laboratory frogs” under the Prime Minister’s Chequers plan, says there is a “gap in the political market”. He warns that he “intends to help fill it”.

Mrs May is coming under growing pressure from Cabinet ministers and within her party to open the door to ditching her beleaguered blueprint for Brexit in favour of a Canada-style trade agreement with Brussels. But she insists her plan “honours the result of the Referendum” and would lead to the UK taking back control of its borders, money and laws.

On Saturday Jeremy Hunt, the Foreign Secretary, publicly piled pressure on to Mrs May by refusing to rule out the prospect of the Government seeking such a deal, despite Downing Street’s insistence that it would “break up the UK” by triggering a backstop requiring a border in the Irish Sea.