Of the prime minister's comments, he said: "Was this an unfortunate case of misreading? It seems extremely implausible. I’m certain that when the PM or more probably some adviser misquotes someone in a draft PMQ response, someone - possibly even the person themselves - checks that the quote is correct. You have to have serious comprehension difficulties to misunderstand the meaning of 'let us suppose'."

He suggested Ms May's claim was "a deliberate lie told to gain political effect" but said he would be willing to accept it was "an honest mistake" if the prime minister or someone from her team could explain how it happened.

He said: "In the scheme of things the issue is very minor, but the prime minister lying whatever the context should be important. But the sad thing is that no one is surprised by this kind of thing any more.

"We in the UK look at Trump’s lying with horror and think this is something uniquely American. But this government has been pulled up countless time for misleading the public by misusing statistics and of course the lies of the Brexiters are shameless."

Mr Wren-Lewis said he had asked the Conservative Party for an apology but was "not holding my breath".