Foreign Secretary Dominic Raab has been branded “deeply dishonest” and accused of "misleading the public" over a no-deal Brexit.
Ben Bradshaw, Labour former Foreign Office minister, said Mr Raab had brought the post of Foreign Secretary “into disrepute”.
The Labour MP has written to the Foreign Secretary demanding he apologises for remarks made on BBC Radio 4's Today programme this week.
He said Mr Raab had claimed the prospect of a no-deal exit from the European Union was “widely discussed and considered a realistic prospect during the 2016 EU referendum” - something he said was “simply not true”.
In the letter, Mr Bradshaw told Mr Raab: “Your pronouncements since taking the job just a few days ago risk bringing this great office of state into disrepute.
“I was astonished to hear you claim on the BBC's Today programme on Monday 29 July that the prospect of a no-deal exit from the European Union was widely discussed and considered a realistic prospect during the 2016 EU referendum.
“You must know this is simply not true.”
He said there appeared to be “no evidence at all” of Mr Raab ever suggesting that leaving the EU without a deal was a likely or possible outcome and accused him of suggesting the opposite.
“This is not a subject for debate, it is a matter of public record,” Mr Bradshaw went on. “For you to now try and claim a democratic mandate for no deal, despite failing to discuss the possibility of such an outcome during the referendum, is deeply dishonest and demeans the office of Foreign Secretary.”
A Foreign Office spokesman said: "The Foreign Secretary has given tangible examples of when all eventualities, including a no-deal Brexit, were raised in the run-up to the referendum in 2016."
Labour MP Ian Murray, a member of the Foreign Affairs Committee, said: "Dominic Raab is continuing the example set by the new Prime Minister of flatly misleading the public when he claims no deal was discussed as a realistic outcome by Leave campaigners including himself during the 2016 referendum.
"It is an insult to the great office of British Foreign Secretary that he holds to twist the truth in this way, and he must be held to account.
"When he appears before the Foreign Affairs Committee on which I sit, I will be asking him about this issue in detail."