The prime minister secured the uneasy support of her cabinet for the draft deal with Brussels after a stormy five-hour meeting on Wednesday night.
Ms May also faces the growing prospect of a vote of no confidence in her leadership of the Conservative Party, as MPs, including Jacob Rees-Mogg, began publishing their letters sent to the party's 1922 committee - calling for the PM to step down.
See below for updates as they happened
Good morning and welcome to The Independent's live coverage of everything Brexit.
↵ Theresa May is already facing crises on numerous fronts, the first being the threat of a raft of resignations after Brexit secretary Dominic Raab quit on Thursday morning.
Here's the latest on Dominic Raab's resignation:
The pound fell heavily against most major currencies after Mr Raab's resignation. Sterling dropped 1.1% to 1.28 US dollars and was 1.2% lower at 1.13 euros.
Northern Ireland minister Shailesh Vara has quit the government in protest at Theresa May‘s Brexit deal, which he claimed would leave the UK in a “half-way house” outside the EU.
Announcing his departure on Twitter, he said: "Today, I have resigned as Brexit Secretary. I cannot in good conscience support the terms proposed for our deal with the EU."
Mr Raab's dramatic resignation will plunge Ms May's leadership into fresh crisis, and comes less than an hour after Northern Ireland minister Shailesh Vara also decided to quit in protest at her Brexit deal.
It also follows widespread speculation that furious Conservative MPs could topple Ms May by submitting enough letters of no-confidence to trigger a leadership challenge.
In his resignation letter, Mr Raab said: "I cannot support the proposed deal for two reasons. First, I believe that the regulatory regime proposed for Northern Ireland presents a very real threat to the integrity of the United Kingdom.
"Second, I cannot support an indefinite backstop arrangement, where the EU holds a veto over our ability to exit. The terms of the backstop amount to a hybrid of the EU customs union and single market obligations.
"No democratic nation has ever signed up to be bound by such an extensive regime, imposed externally without any democratic control over the laws to be applied, nor the ability to decide the exit arrangement.
Esther McVey has resigned as work and pensions secretary
Esther McVey quits government over Brexit dealWork and Pensions Secretary Esther McVey has become the latest cabinet minister to quit the government over Brexit a fresh blow to Theresa May's authority. The Brexiteer said prime minister's draft Brexit deal "does not honour the result of the referendum'' and she "could not look my constituents in the eye" over the plans. Her departure comes shortly after the shock resignation of Dominic Raab, the Brexit secretary, which raises major questions over the future of Ms May's leadership. More follows…
Considering we're on resignation watch this morning - after two cabinet ministers have resigned from the government over Theresa May's deal - this is raising many eyebrows in Westminster.
Pound plummets sharply after Dominic Raab resigns as Brexit secretaryThe pound dropped sharply on Thursday morning after Brexit secretary Dominic Raab resigned.Sterling was down more than 1 per cent against both the dollar and the euro, moments after the announcement of Mr Raab's resignation which blew a hole in the theory that Theresa May had managed to unify her Cabinet around a Brexit deal.The pound was down 1.17 per cent against the dollar at $1.2841 and 1.25 per cent down against the euro at €1.1341.
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