Pressure is building on U.K. Prime Minister Theresa May to ditch her Brexit plan or face a catastrophic defeat in Parliament.

Britain and the European Union have been edging toward an agreement after 16 months of talks, with the aim of getting a deal wrapped up at a summit in November. But as domestic opposition builds, momentum seems to be fading for getting a deal done quickly. The pound fell.

The Cabinet had been expected to meet as soon as Monday to sign off on May’s plans, but late on Sunday there was no sign of further progress, according to three people familiar with the matter. If May wants a deal sealed in November — as investors and businesses hope — this week is probably the last chance to corral her divided Cabinet.

Getting any divorce deal through a bitterly divided Parliament was always going to be May’s biggest challenge. But as the various factions who oppose May’s approach step up their warnings, it’s looking even trickier than her whips may have calculated.

Pro-Brexit Conservative lawmakers joined forces on Sunday with the Northern Irish party that props up May’s minority government. They threatened to reject the deal she’s working on, even if she persuades the Cabinet to approve it in the coming days.

“If the government makes the historic mistake of prioritizing placating the EU over establishing an independent and whole U.K., then regrettably we must vote against the deal,” Steve Baker, a former Conservative minister, and Sammy Wilson, Brexit spokesman for the Democratic Unionist Party, wrote in the Sunday Telegraph.

Brexiteers want a clean break with the EU so Britain can pursue its own trade deals around the world and regain control over regulations and legislation. They fear that the guarantees May’s offering to avoid checks at the border with Ireland risk tying the U.K. to European rules indefinitely. Northern Irish lawmakers are concerned the region will end up being treated differently to Britain.

A New Front

On the other side of the debate, there’s growing criticism of May among pro-EU Conservatives, with the shock resignation of Jo Johnson as transport minister on Friday triggering speculation that others could follow. Johnson, the pro-EU brother of Brexit-backing former Foreign Secretary Boris Johnson, called for a second referendum as he said May’s handling of the talks had left Britain with a choice between handing over even more sovereignty than EU membership required, or accepting the chaos of no deal.

Former Education Secretary Justine Greening weighed in on Sunday, backing Johnson’s move and reiterating her call for another plebiscite. There’s still no majority in Parliament for a re-run of the 2016 vote, but if more pro-EU Tories come out in favor it will make it even harder for May to get her deal approved. Lawmakers campaigning for a do-over see an opportunity to push for one if May’s divorce treaty is thrown out by Parliament.

May’s whips hope that a number of Labour lawmakers will end up voting for her deal, particularly those who represent pro-Brexit constituencies. But Labour’s Brexit spokesman Keir Starmer again pushed back against the idea on Sunday, saying there’s no obligation for members of Parliament to surrender to a bad deal out of fear of crashing out of the EU without one.

On Monday Mayor of London Sadiq Khan, an influential figure in the Labour Party, urged his party in the House of Commons to reject May’s deal. He told Bloomberg TV he’d asked EU negotiator Michel Barnier to work on the possibility of extending Article 50, the mechanism by which the U.K. leaves the bloc in March next year.

Irish Backstop

The main battle remains over the Irish backstop, which would prevent the return of a hard border on the island of Ireland by allowing all of the U.K. to remain in a customs union after the post-Brexit transition period ends in December 2020. It’s meant to be a last-resort measure, but plenty of people on both sides think it’s likely to be invoked.

Britain and the EU are working on a review clause, involving both sides, that would allow Britain to leave a customs arrangement. But one Brexit backer, House of Commons leader Andrea Leadsom, warned Sunday that an arrangement that left Britain “trapped” against its will would be impossible to sell to Parliament.

In a surprise concession, Jacob Rees-Mogg, who leads the European Research Group of pro-Brexit Tory MPs, made what he called a proposal to break the impasse with the EU. Under “No Deal Plus,” Britain would offer to pay 20 billion pounds ($26 billion) — half the divorce bill currently envisaged — to make its departure “as amicable as possible” and leave following a 21-month transition period.

> La suite sur le National Post.