Labours shadow Brexit secretary Sir Keir Starmer this morning said his party would not be supporting the “second-rate” withdrawal agreement struck by the PM.
He said the Brexit deal, which Mrs May announced had received the backing of her cabinet last night, was a "miserable failure of negotiation" after two years of talks with the EU.
He told ITVs Good Morning Britain: "It's a chaotic ending and the root cause is the utter division on the Conservative benches."
"We will vote against this deal because it does not meet our tests. I dont think anybody would sign up to a document without knowing where it was heading.”
Labours position increases the likelihood of the PMs withdrawal agreement being voted down by MPs in the House of Commons, where her wafer-thin majority puts its passage in doubt.
Meanwhile, Northern Ireland minister Shailesh Vara has resigned from the cabinet after deciding he could not back the PMs plan for leaving the EU.
The Tory MP for North West Cambridgeshire, who was appointed to his ministerial role in July, said the deal struck by Mrs May did not align with what the British public voted for.
DOUBLE BLOW: Labour has vowed to vote down the deal and a cabinet minister has resigned (Pic: DS)
FIRST RESIGNATION: Shailesh Vara is the first minister to resign over Theresa May's government (Pic: WIKIPEDIA)
LETTER: Vara said the deal leaves the UK in a 'halfway house' (Pic: TWITTER)
In his resignation letter to the PM, he wrote: “The EU referendum offered a simple choice – either stay in or leave the EU.
“The vote was decisive with the UK public voting to leave, and that is what we, their elected representatives, must deliver.
“The agreement out forward, however, does not do that as it leaves the UK in a halfway house with no time limit on when we will be a sovereign nation.”
Vara, who supported Remain in the 2016 referendum, said the people of the UK “deserve better” than the compromise draft deal currently on the table.
His resignation could be the first of a wave of departures from the government over the polarising agreement Mrs May has reached with EU negotiators.
PLEASED AS PUNCH: Smiling Michel Barnier and Donald Tusk present the withdrawal agreement (Pic: GETTY)
IN THE NATIONAL INTEREST: Theresa May secured support for her deal from the cabinet (Pic: GETTY)
“We will vote against this deal ”
His resignation could be the first of a wave of departures from the government over the agreement Mrs May has reached with EU negotiators.
Her deal has been savaged by Remain and Leave-supporting MPs across the political spectrum, while in Europe, it appears to have gone down well.
Brexit-backing Tory MPs on the backbenches have threatened to unseat Mrs May by sending no confidence letters to Sir Graham Brady, chairman of the 1922 Committee.
Meanwhile, the EU council president Donald Tusk this morning announced that an extraordinary summit in Brussels on November 25 will take place to finalise the UKs withdrawal agreement.
DOCUMENT: Barnier holds the draft agreement of the withdrawal deal (Pic: GETTY)
Striking a tone of caution, however, Tusk suggested the summit may be derailed in the event something “extraordinary happens”.
The PM cleared the first hurdle when cabinet ministers finally approved the draft terms of her agreement with Brussels at a stormy five-hour meeting on Wednesday.
Speaking outside 10 Downing Street minutes after the meeting concluded, she acknowledged she faced "difficult days ahead" as she attempts to win round critical MPs.
"I firmly believe, with my head and my heart, that this is a decision which is in the best interests of the United Kingdom," she said.
"At the same time she warned Brexiteers that if they failed to back her plan they risked ending up with "no Brexit at all".</span>
ARCH BREXITEEER: Rees Mogg has urged Tory MPs to vote against the deal (Pic: GETTY)
Following the release of the 585-page agreement document, Jacob Rees-Mogg – the leader of the pro-Brexit European Research Group – wrote to all Tory MPs urging them to vote against it.
Rees-Mogg said that he was not among those MPs who had written to Brady, but suggested he could be "very close" to doing so.
"Certainly this has dented my confidence," he told ITV's Peston programme. "Politics depends on trust and this document is shattering to trust."
While the Cabinet agreed to collectively support the agreement, there was speculation that some ministers were so unhappy that they could still quit in protest.
Reports suggested as many as a third of the 28 ministers attending the meeting in No 10 voiced doubts about the deal.
Nick Timothy, Theresa May's former chief of staff, wrote in the Daily Telegraph that Parliament will "surely" reject the proposal.
"The proposal presented to Cabinet is a capitulation," he wrote.