Dominic Raab has resigned from the Cabinet in protest at the draft Withdrawal Agreement with the EU signed by Theresa May.

The former Brexit Secretary said he believed the deal “presents a very real threat to the integrity of the United Kingdom”.

Raab said he could not support a backstop arrangement which the UK could not end without the EU agreeing.

May is due to present her deal on Britain’s EU exit to the Commons this morning amid speculation she could face a vote of no confidence from Tory MPs.

The 585-page deal will provide the basis of a legally binding treaty. It covers the future rights of EU citizens living in the UK and UK nationals in the EU, the UK’s £39bn ‘divorce’ settlement, as well as protocols on Gibraltar and the UK sovereign base areas in Cyprus.

It also provides for a transition period after the UK leaves in March 2019 running to the end of 2020, with the option of a one-off extension if more time is needed to conclude an agreement on the future relationship.

Crucially it also covers the so-called “backstop” intended to ensure there is no return to the hard border between Northern Ireland and the Republic if negotiations on the future relationship have still not been completed.

In his letter to the PM, Raab said: “I cannot reconcile the terms of the proposed deal with the promises we made to the country in our manifesto at the last election. This is, at its heart, a matter of public trust.

“I appreciate that you disagree with my judgment on these issues. I have weighed very carefully the alternative courses of action which the government could take, on which I have previously advised.

“Ultimately, you deserve a Brexit Secretary who can make the case for the deal you arc pursuing with conviction. I am only sorry, in good conscience, that I cannot.”

He added: “My respect for you, and the fortitude you have shown in difficult times, remains undimmed.”

Shailesh Vara also quit as Northern Ireland Minister this morning, saying he cannot support May’s Brexit agreement, which he said “leaves the UK in a halfway house with no time limit on when we will finally be a sovereign nation”.

Pro-EU Tory MP Anna Soubry said Raab’s resignation marked “the end of the PMs Withdrawal Agreement”.

“This is v serious the PM will clearly be considering her position. My own view is that we need a Govt of National Unity and we need it now,” she tweeted.

May cleared the first hurdle when Cabinet ministers approved the draft terms of her agreement with Brussels on Wednesday.

But several of the ministers round the table are reported to have spoken up against the deal.

Raab’s resignation has dealt a serious blow to her chances of winning a Commons vote.

Labour, the SNP, the Lib Dems, her DUP allies as well as Brexiteer and pro-EU Tories have all indicated they will vote against the agreement.

A move by Brexiteer Conservatives unhappy with the deal to try and oust May as leader is now said to be imminent.