Prime Minister Theresa May’s tenuous hold on power suffered a further blow Thursday evening as her Brexit negotiating plan for exiting the European Union (EU) was again rejected by MPs.

Just two weeks ago, pro-Tory papers were crowing about May’s “triumph” after she overturned a previous defeat when MPs rejected her plan by a record margin of 230 and secured a slim parliamentary majority to seek concessions from the EU on the post-Brexit Irish border. But this backing evaporated Thursday, when May’s motion urging endorsement of her continued negotiations was defeated by 303 votes to 258 with nearly a quarter of Tory MPs, 67, abstaining and five voting against her deal.

May was sunk by the combined efforts of the hard-Brexit European Research Group (ERG), who took a “collective decision” to abstain and by nine pro-EU Tories, including Anna Soubry and Dominic Grieve. The Brexiteers voting against were Peter Bone, Sir Christopher Chope, Philip Hollobone, and Anne Marie Morris, as well as pro-Remain Tory, Sarah Wollaston.

The vote was non-binding but shows that May is still unable to win the backing of a majority of MPs for her plans—making it even more difficult to secure concessions from the EU.

May has still been unable to win support among EU leaders for a change in the wording of the agreement previously reached regarding the Irish border that would satisfy her substantial Eurosceptic wing. The Brexiteers don’t want even a temporary backstop in place that would keep Northern Ireland in the EU customs union, until an all-encompassing future deal could be reached between the UK and EU.

This left May putting a motion calling only for support of the motion passed January 29 instructing her to return to Brussels to agree “alternative arrangements” to replace the existing backstop plan and failing to get this passed.

The motion also called for an endorsement of a vote in Parliament last month that ruled out leaving the UK in a “no-deal” Brexit, forced to trade on World Trade Organisation terms. This is the bare minimum demanded by pro-Remain Tories and all the main opposition parties and has a clear majority in Parliament but is anathema to the ERG.

These intractable divisions threaten a split in the party, with most Tory MPs supporting a “soft-Brexit” and a maintenance of relations with the EU.

Government business minister Richard Harrington said after the vote that the ERG should join the new Brexit Party being promoted by former UK Independence Party leader Nigel Farage. The ERG “were drinking champagne to celebrate her losing her deal and I regard that as being treachery,” he said.

Parliament’s pro-EU wing is determined that the ERG must not prevail and are lined up to back an amendment from the Blairite Labour MP Yvette Cooper on February 28, when May has authorised another vote to take place on her negotiations.

The amendment would give Parliament the power to prevent May from carrying out a no-deal Brexit. One Tory minister commented, “We are determined that talks [with the EU] can’t continue into March.” Airing the concerns of dominant sections of big business and manufacturing, he added, “We will make sure business is not further devastated. The PM has done her best but we can’t allow the European Research Group and others to take negotiations into March.”

Divisions over Brexit cut across party lines, leading to the sizeable rebellion suffered by Labour leader Jeremy Corbyn. Thursday saw 41 Labour MPs ignore a party whip instructing them to oppose a Scottish National Party amendment calling for Brexit to be delayed by at least three months.

The rebellion was led by Blairites who have been seeking Corbyn’s removal since he became leader in 2015. Their opposition has focused on attacking his Brexit policy, which they say is enabling May to get her deal through—along with manufacturing claims that the Labour leader is a facilitator of anti-Semitism within the party.

Corbyn supports a soft-Brexit, but has not specifically demanded, as have some of his shadow cabinet, that a second referendum “People’s Vote” be required on Brexit. He has stuck to the insistence that Labour is seeking a general election and only failing this will other options, including a second referendum, be considered.

Addressing the crisis, the pro-Labour New Statesman commented this week on “Why, for Corbyn or May, breaking the Brexit deadlock would also mean splitting their parties.” Both leaders were seeking a “Brexit deal that is acceptable to the European Union and can pass the House of Commons, and the price for each leader is shattering his or her party, potentially permanently.”

Of the divisions tearing apart Labour, the New Statesman wrote, “If Labour lets May’s deal through, it would also provide the perfect pretext for a split by ‘the Six’—the anti-Corbyn MPs who want to set up their own party.”

Earlier this month, the pro-Remain Observer reported that it had been told “at least six” leading Labour right-wingers were preparing to set up a breakaway party. However, Thursday’s rejection of Corbyn’s whip revealed that there are substantially more than six Blairites that may be prepared to quit.

One of Corbyn’s long-time opponents, Chris Leslie—whose constituency party members passed a vote of no confidence in him last year—said after Thursday’s vote, “I certainly feel that we are being played for fools by the leadership of the Labour party on this particular issue because by now we should have reached the option of a public vote with the option of remaining in the European Union …”

One of the Labour right’s main figureheads is Chuka Umunna. The Financial Times noted Thursday that he is among a “core group” of backbenchers who have “been discussing a breakaway party for months.”

Even the mechanics of how such a party would be established are being made known to the main pro-Remain voice of finance capital. The FT reported that “Under one plan, at least one MP would step down to prompt a by-election. Winning back his or her seat under the banner of a new party would prove the group could ‘win elections,’ a backbencher said. At that point, the breakaway faction would try to persuade other MPs to leave Labour and join them.”

From Umunna’s latest statements, any such moves would need to be coordinated with pro-EU Tories also standing down in protest at the danger of a no-deal Brexit. Umunna warned on his own website prior to Thursday’s votes that there were just “46 days until Brexit … If ministers want to influence the outcome of Brexit, now is the sensible time to resign and vote accordingly, otherwise it will be too late.”

Umunna insisted, “in order to get a cross-party amendment through which paves the way for Parliament to stop the government running down the clock—which risks the UK falling off the cliff without a deal--we must both reduce the [pro-Brexit] Labour rebellion and increase the Conservative one.”

Stating that he was in talks with sympathetic Tory ministers, he revealed that several “are considering their positions and are now contemplating resigning from government …”