Foreign Secretary Jeremy Hunt has issued a stark warning to Tory MPs they risk losing Brexit altogether if they fail to back Theresa May's deal in the crunch Commons vote on Tuesday.

Mr Hunt said there was now "wind in the sails" of the opponents of Brexit and that it would be "devastating" for the Conservatives if they failed to deliver on their commitment to take Britain out of the EU.

His warning came after Brexiteer Tories and their DUP allies warned the Government was heading for an "inevitable" defeat on Tuesday unless it can secure last minute concessions from the EU on the Northern Ireland backstop.

But with little sign of a breakthrough in talks in Brussels, Mr Hunt said MPs could not "wish away the parliamentary arithmetic" and that any alternative to Mrs May's deal agreed by the Commons was likely to be "less appealing" to Brexiteers.

"People worry about us being trapped in the customs union by the backdoor but we could end up in the customs union by the front door if we get this wrong," he told BBC1's The Andrew Marr Show.

"We have an opportunity now to leave on March 29 or shortly thereafter and it is very important we grasp that opportunity because there is wind in the sails of people trying to stop Brexit.

"If you want to stop Brexit you only need to do three things - kill this deal, get an extension and then have a second referendum.

"Within three weeks people could have two of those three things and quite possibly the third one could be on the way through the Labour Party. We're in very perilous waters."

Mr Hunt said that if Brexit was derailed, voters would hold the Conservatives responsible for failing to deliver on the outcome of the 2016 referendum.

"They are going to say there was a party that promised to deliver Brexit, we put them into Number 10 and they failed. The consequences for us as a party would be devastating," he said.

"This is a very important moment for us. There is a risk and a possibility that we end up losing Brexit if we get the votes wrong in the next couple of weeks."

There was little sign however that Brexiteers were willing to fall into line without changes to the deal which suffered a crushing 230-vote defeat when Mrs May put it to the first "meaningful vote".

In a joint article for The Sunday Telegraph, Steve Baker, the deputy chairman of the pro-Brexit Tory European Research Group, and DUP deputy leader Nigel Dodds said she could be heading for another three-figure defeat.

Former Brexit secretary Dominic Raab, who quit over the Brexit deal, acknowledged the Prime Minister's position was "precarious" but said it would be even worse if Brexit was delayed.

Mrs May has said if the Government loses on Tuesday, there would be further votes on Wednesday on whether the UK should leave with no-deal and on Thursday on whether they should seek an extension to the Article 50 withdrawal process.

Mr Raab said that if that happened, it was essential she ordered Tory MPs to vote to leave open the option of a no-deal break.

"We've absolutely got to whip the vote to keep our manifesto pledges. How can a government function that doesn't keep its promises?" he told Sky News's Sophy Ridge on Sunday programme.

Mr Raab, who has been touted as a possible successor to Mrs May if she is forced to step down, refused to be drawn on his own leadership ambitions.

But asked if he thought Mrs May would still be Prime Minister by Christmas, he said: "I don't know. She has said she is going to step down. I would like to be able to see her do that in a way which is in terms of her own choosing.

"I think the Government has found itself in a precarious situation. If the Government extends Article 50 or tries to reverse the Brexit promises that we have made, I think that situation would get even trickier."

For Labour, shadow Brexit secretary Sir Keir Starmer said he did not expect Labour to try to amend the "meaningful vote" motion on Tuesday.

"I don't know whether something dramatic will happen in the next 24 hours but unless it does, exactly the same deal is going to be put before Parliament," he told the Sophy Ridge On Sunday programme.

"That is eight weeks of failure to come back and present exactly what was rejected, so on Tuesday that has got to be exposed."

Sir Keir said he expected there would still be an opportunity for MPs to vote for a second referendum in the days ahead, either on a Labour amendment or one tabled by backbenchers.

"It doesn't mean that a public vote is gone. It doesn't mean we won't come to it. We will have to work with others," he said. "There is going to be plenty of opportunities for amendments."