THERESA May has suffered another humiliating Commons defeat after MPs again voted down her latest Brexit plans.

On another dramatic day at Westminster, MPs voted by 303 to 258 against the motion endorsing the Government’s approach.

The defeat came after the pro-Brexit Tory European Research Group (ERG) announced they had taken a “collective decision” to abstain. Furious members of the group said supporting the motion would have amounted to an endorsement of efforts to rule out a no-deal Brexit.

Business Minister Richard Harrington accused members of the group of “treachery” over Brexit.

Referring to the ERG, the minister told The House magazine: “The Prime Minister has done a pretty good job of standing up to them up till now, but they were drinking champagne to celebrate her losing her deal and I regard that as being treachery.”

He added that members of the group should consider moving over to Nigel Farage’s new party.

The defeat now means the Prime Minister cannot continue to claim she has a Commons mandate for her attempt to renegotiate the backstop.

Following the vote, both Labour leader Jeremy Corbyn and SNP

Westminster leader Ian Blackford called for May, who was not present during the afternoon’s debate or vote, to come to the Commons and set out her response.

Blackford urged the second meaningful vote on the Brexit deal to be brought forward to next week. He also hit out at Labour who failed to back his party’s amendment calling for Brexit to be delayed by no less than three months.

“Westminster is failing Scotland – as the UK Government runs headlong towards economic and constitutional catastrophe with Brexit,” Blackford said later. “This was another humiliating defeat for the Prime Minister. Once again, Tory and Labour MPs have joined together to vote against Scotland’s interests. With just 43 days to go until the UK crashes out of the EU, it is utterly shameful that they have put party before country by voting down SNP proposals to extend Article 50 and prevent a disastrous no deal Brexit.

“Leaving the EU with Theresa May’s bad deal or with no deal at all would be devastating for Scotland – hitting Scottish GDP by up to 9%, putting 80,000 jobs on the line, and costing our economy £12.7 billion a year – the equivalent of £2300 lost for every single person in the country.”

He added: “Scotland didn’t vote for Brexit – and we must not be dragged out of the EU against our will. If Labour are intent on being the midwives of a Tory Brexit then Scotland must find a way to protect our own interests.”

Nicola Sturgeon also attacked Labour for failing to back the SNP amendment and said Jeremy Corbyn’s party could end up “midwives of a Tory Brexit”.

Pointing to the SNP amendment which was defeated by 315 to 93 votes, she wrote on Twitter: “Good to know that some Labour MPs had courage of convictions to vote for @theSNP amendment to extend Article 50. The fact that the majority didn’t underlines concern that Labour leadership could be gearing up to be the midwives of a Tory Brexit.”

During the debate May was warned by senior backbenchers to stop pursuing the “meaningless” amendment to alter the backstop, and instead focus on extending Article 50 and ruling out no deal.

Former chancellor Ken Clarke said the Prime Minister should not be trying to make changes to the Brexit deal to appease the ERG, saying they will “reject anything we come back with because some of them want to leave with no deal”.

The veteran Conservative member for Rushcliffe and Father of the House said: “The Government has pursued one of the factions on our side of the House, we have a kind of breakaway party within a party, bit like Momentum really, got their leader, got their chief whip.

“They are ardent right-wingers, and the Government has set off in pursuit of these bizarre negotiating tactics that some of them say, though some of them seem to want to leave with no deal, because any agreement with foreigners from the continent is a threat to our sovereignty.”

He said that is “the wrong group to pursue”, and called the Brady amendment – which called for an alternative to the backstop – “meaningless”. His view was echoed by former minister Anna Soubry, who said the speech to open yesterday afternoon’s debate by Brexit Secretary Stephen Barclay “chilled me to the bone”.

Accusing the Tory Party of being “in hock to the party within a party, the ERG”, the prominent pro-EU MP said the Cabinet minister had “tossed out red meat to keep them on board”.

Fellow Tory backbencher Sir Oliver Letwin said he had come to the conclusion that the Prime Minister would actually prefer to “head for the exit door without a deal”, adding: “Which the Secretary of State informed us is the policy of HM Government in the event that her deal has not succeeded, that is a terrifying fact.”

After the vote Jeremy Corbyn said: “Tonight’s vote shows there’s no majority for the Prime Minister’s course of action, and yet again her government has been defeated.”