Talks between the Conservative government and Labour opposition on an alternative Brexit deal resume today, with a meeting between Prime Minister Theresa May’s deputy, David Lidington, and Shadow Brexit Secretary Keir Starmer.

This week’s talks, described as the final round, take place under conditions of acute crisis for May, with her dysfunctional government and party losing more than 1,300 council seats and control of 44 councils in last week’s local elections. With Labour making smaller losses, Labour leader Jeremy Corbyn stressed that the lesson was that the electorate want Brexit to be implemented.

However, such are the divisions over Brexit policy wracking both parties that these talks could flounder. Tensions surfaced again at the weekend, as the latest offer from May to Labour was leaked to the Sunday Times and other newspapers.

The leaks outlined that May is seeking to win the support of the Tories’ pro-Remain wing and a large proportion of Labour MPs by offering Labour a temporary customs union with the European Union (EU)—that would be in place only until the next election scheduled for 2022. May is attempting to sell this on the basis that during this period, the UK would be able to access the benefits of being in the customs union while still negotiating some trade agreements with other states and not signing them until a new government takes office.

If agreed, this would be added to the 26-page political declaration on the future relationship with the EU that accompanies the main withdrawal agreement already in place since last November.

After May was unable to pass her EU deal in parliament, even after three attempts, Corbyn dropped any talk of demanding a general election and came forward to join the Tories in talks in his guise of a trusted statesman of the ruling elite.

However, such is the collapse of May’s government—with Defence Secretary Gavin Williamson being sacked just last week—that Labour must perform a careful balancing act. The Financial Times reported that “Some allies of Jeremy Corbyn…are anxious about ending up in a ‘national government in all but name’ but without any ministerial posts—sharing the blame for any Brexit fallout with the Tories.”

Speaking on the BBC’s Andrew Marr Show , Corbyn’s closest ally, Shadow Chancellor John McDonnell, said he did not trust May because she leaked her proposals to the Sunday Times and that reaching a deal with her government was like “trying to enter into a contract with a company which is about to go into administration.”

On the leaking of May’s plan, McDonnell said Labour had worked in the national interest for weeks to maintain confidentiality over what was being tabled but that “she’s [May] blown the confidentiality we had. … I actually think she’s jeopardised the negotiations for her own personal protection.”

But his main opposition to May’s plan was that it didn’t satisfy the needs of big business. He told Marr, “Where we are at the moment is: yes, we want a customs union, but a permanent and comprehensive customs union and the reason for that—why we’ve become the party of business—is that businesses want security not just for a few months up to an election but they want it permanently” (emphasis added).

While Labour’s substantial Blairite wing of MPs could back the offer, the pro-EU Guardian reported that their support was conditional on a public vote on any final deal. It noted that 104 opposition MPs, including 66 from Labour, had informed May in writing they would only back a deal if it was put to a “confirmatory referendum.” The Guardian, somewhat optimistically, cited the Blairite-led People’s Vote campaign as believing “there are actually more like 150 to 180 Labour MPs out of 229 who will refuse to back a deal struck with May unless there is a confirmatory vote.”

Much of the media again point to the possibility of a Tory split over Brexit being in the cards, but Labour could just as easily fracture. The seven pro-Remain Blairites who split with Labour in February to found The Independent Group (TIG)/Change UK, are only a fraction of the broader group of acolytes of Tony Blair and Gordon Brown led by deputy Labour leader Tom Watson. Watson again called for a second referendum at the weekend, stating “a very large number of our members think the people should decide on what that deal looks like.”

The intervention of McDonnell and Labour’s pro-Remain wing spooked the markets, with Sterling fallen more than 0.5 percent by midday Monday. The Financial Times commented that this was in response to senior Labourites casting “doubt on the prospect of a cross-party Brexit deal over the weekend, cooling expectations that…May was nearing an agreement with opposition MPs.”

May’s problem in reaching an agreement with Corbyn is, however, compounded by the bitter response of her party’s hard-Brexit wing at the prospect of even temporarily remaining in the EU’s customs union.

Nigel Evans, executive secretary of the 1922 Committee of backbench Tories, told the BBC’s John Pienaar, “If there is a compromise that turns out to be a kind of ‘Brexit in name only’ involving anything close to a customs union, there would be more than 100 Tory MPs who would never support it.”

Sir Graham Brady, the 1922 Committee chair, warned in the pro-Brexit Telegraph that agreeing on a customs union deal with Labour “might pull in enough Labour votes to allow an agreement to limp over the line but the price could be a catastrophic split in the Conservative party and at a time when the opposition is led by dangerous extremists, the consequences for our country would be unthinkable.”

The Telegraph denounced May in its editorial, declaring that she “is determined to deliver something called Brexit without being overly fussed about what it entails. To that end, she is relying on Labour to agree a pact. But to do so she will have to make such concessions, notably on the customs union, that the Tory party would be blown apart.”

The Sun political editor Trevor Kavanagh presented the possibility of a Corbyn led-government in apocalyptic terms, writing that Labour “aims to destroy the Tories, undermine the Western way of life and turn Britain into a Marxist state.”

Pointing out that that an all-time high 82 percent of Tory members polled by ConservativeHome wanted May to go, the Sun editorialised Monday, “A potential deal with Jeremy Corbyn reeks of an administration that has run out of road. … May must now accept the game is up and announce a departure date.”

After stating in his column that any recovery of the Tory party “depends on national leadership,” Brady, according to reports, will demand May set out a timetable for her exit as party leader and prime minister. He chairs a committee able to change party rules prohibiting a confidence vote on May for 12 months after she survived the last such vote in December.