Conservative MP Dominic Grieve has said that Remain would have to be an option in a second referendum because “people in a democracy are allowed to change their minds”.
This comes as EU leaders granted the UK a six month extension until October 31 in order to give enough time “to find the best possible solution”.
The former attorney general told talkRADIO’s Julia Hartley-Brewer: “I may consider it to be a flawed project but if the electorate decided to leave on the terms that were being offered to them in the referendum then that would be it.
“We could put in place the necessary mechanisms for leaving almost immediately afterwards. We would not need any further parliamentary debate.
“I want Remain on the ballot paper because people in a democracy are allowed to change their minds.
“I would wish to Remain on the ballot paper, in fact I think it is essential.”
Under the terms of the new agreement, the UK can leave at any time if the Withdrawal Agreement reached last November is ratified by the Houses of Parliament.
If the UK fails to take part in elections to the European Parliament on May 23-26, it will automatically leave without a deal on June 1.
Mr Grieve said that the EU wanted to see “progress towards a definite end” with this further extension.
He added: “What they don’t want is a continuing lurching from one departure crisis to another.”
The MP for Beaconsfield said he was “pessimistic” about Labour and the government agreeing a deal, despite continued talks between the shadow Brexit secretary Keir Starmer and cabinet office minister David Lidington.
He said: “In view of the number of months’ extension we have got, we have got to make use of it, either to find a deal that is acceptable - I am very pessimistic about that because I think it is most unlikely that Labour will sign up to any deal of the prime minister’s - or alternatively we have got to go back to the people and put the options to them.”