A row has erupted after the Prime Minister is alleged to have flew to Berlin to share her exit plan with Angela Merkel before she revealed it to her Cabinet at her Chequers retreat in Buckinghamshire.

When quizzed over possible alterations to the Brexit blueprint, Mrs May is said to have made an extraordinary excuse saying: “No that’s not possible.

“Because I’ve already cleared the existing text with Mrs Merkel.”

Downing Street sources strongly refuted the claims but in the Spectator, journalist Charles Moore wrote: “At Chequers, I hear, one of her responses to suggested changes in her blueprint was to say, ‘No, that’s not possible, because I’ve already cleared it [the existing text] with Mrs Merkel’.”

Mrs May flew to Berlin last Thursday – the day before crunch talks at Chequers – to hold a meeting with Mrs Merkel.

Number 10 has refused to comment on the claims.

Last night leading Tory Brexiteer Jacob Rees-Mogg said it would unconstitutional of…