Rory Stewart’s stance on Brexit makes him unfit to be Mayor of London, according to one of his rivals.

Liberal Democrat Siobhan Benita said Mr Stewart had “shown his true colours” by refusing to back a vote in Parliament that aimed to prevent a no-deal Brexit.

The Letwin Amendment – named after its proponent, former Conservative minister Sir Oliver Letwin – states that the Government must ensure legislation to enact Brexit is in place before Parliament approves its new deal.

The amendment passed by 322 to 306 votes during an extraordinary parliamentary session on Saturday.

It closes a loophole that could have seen MPs back Boris Johnson’s deal, only for the UK to crash out of the EU at the end of the month because the legal levers for the deal were not in place.

The Prime Minister has now written to the EU to request an extension, meaning the UK may not leave on October 31. But he did not sign the letter, and send a second – signed – letter saying he believed a delay would be a mistake.

In Parliament on Saturday, Mr Stewart voted with the Government to oppose Sir Oliver’s amendment.

The former Conservative MP was expelled from the parliamentary party last month for voting against the Government to oppose no deal Brexit.

He has since resigned from the Conservative Party, and announced that he will stand down from Parliament at the next election and run to be London Mayor.

Ms Benita said his views were out of step with the capital.

She said: “It’s staggering that someone running to be Mayor of liberal, remain-voting London couldn’t even bring himself to back an amendment which merely asked for extra time to scrutinise Boris Johnson’s deal and to prevent what is universally recognised to be a catastrophic no-deal Brexit.

“How can he claim to speak for London and talk about compromise when he backs an extreme version of Brexit that will so damage our capital city?

“London is my home. I would never compromise on its future.

“I can’t really understand why he’s in this election and I think Londoners are wondering the same.”

Mr Stewart said the country was in “Brexit purgatory” and needed a resolution.

Posting on Twitter, he said: “The longer it drags on, the more we are pushed – partly by politicians – into hostile and uncomprehending tribes.

“It is getting worse. We must finally find the strength to end this division – and that must mean having the courage to compromise.”

Parliament will vote today or later this week on Boris Johnson’s Brexit deal.