The headlines for Jeremy Corbyn’s speech on Monday are about his U.K. Labour Party’s Brexit policy. The subtext is Prime Minister Theresa May’s future.

If Corbyn follows the urging of his lawmakers and senior Labour spokesmen and says Labour supports a customs union with the European Union, the stage would be set for a showdown in which a rebellion by a small number of pro-Europeans in May’s Conservative Party could derail her strategy.

Extracts of Corbyn’s speech released in advance contained no mention of a customs union, although his office said he would be talking about it. Instead, they reflected Corbyn’s own deep ambivalence about the EU. 

“The European Union is not the root of all our problems and leaving it will not solve all our problems,” he’ll say in Coventry, central England. “Likewise, the EU is not the source of all enlightenment and leaving it does not inevitably spell doom for our country.”

A lifelong euroskeptic, Corbyn’s desire to precipitate a crisis for May might be guiding his feelings about Europe. Amendments to Brexit legislation currently going through the House of Commons could bind May’s hands on this unless she defeats them. The change in stance by Labour, which previously only kept open the “option” of a customs union, exposes her to that possibility.

Crisis for May?

That in turn increases the likeliness of another election at a time when polling indicates the parties are neck-and-neck.

Remain-supporting rebels in May’s Conservatives also want to see Britain retain a customs deal with the EU after leaving the bloc. May’s fragility was laid bare in December when those rebels teamed up with Labour to defeat her in Parliament, ensuring lawmakers will have a meaningful vote on the final deal she strikes with the EU.

May has ruled out any form of customs union with the EU after Brexit, saying that would curtail Britain’s ability to broker new trade deals. If she abandons that stance, she risks alienating another faction within her party: the hardcore Brexiters led by Jacob Rees-Mogg, the bookmakers’ favorite to succeed her. 

Playing Games?

One of them, former party leader Iain Duncan Smith, told the BBC on Sunday that his message to Tories who might back the new Labour position: “be very careful on this one because you’re being invited into a Labour Party tactical game which will actually end up in real damage to the United Kingdom.”

May will have to fend off those who want Britain to stay in a customs pact. Former Chancellor of the Exchequer Ken Clarke and former Business Minister Anna Soubry have proposed an amendment to May’s Taxation Bill that would oblige the premier to stay in an EU customs union after Brexit. They’re backed by Labour lawmakers including Chuka Umunna, and the proposals are similar to those advanced by Labour’s leadership.

“Whether it’s our amendments or the cross-bench amendments, crunch time is now coming for the prime minister because the majority of Parliament does not back her approach to a customs union,” Labour’s Brexit spokesman, Keir Starmer, told BBC TV on Sunday.

‘Unanimous’ Agreement

Starmer said the shadow cabinet is “unanimous” in agreement on its proposal for a post-Brexit deal with the EU that does “the work of the current customs union.”

Corbyn will signal that a Labour-led government would seek a bespoke deal with the EU, citing the examples of Switzerland, Norway and Turkey. In one breath, he’ll seek a close relationship with the bloc, while signaling in the next that continued membership would prevent him doing some of the things he’d like to do in government.

“Labour would negotiate a new and strong relationship with the single market that includes full tariff-free access and a floor under existing rights, standards and protections,” he’ll say. “We would also seek to negotiate protections, clarifications or exemptions, where necessary, in relation to privatization and public service competition directives, state aid and procurement rules.” 

The more mainstream and centrist Labour lawmakers were encouraged by the prospect of a shift in Labour’s Brexit stance. Umunna tweeted it was “very welcome.” Chris Bryant, another backbencher seeking to soften Brexit, said in a text message that he was “delighted,” while a third, Peter Kyle, urged the party to go further by endorsing continued membership of the single market.

“Businesses, universities, and tourists need to plan ahead,” Kyle said by phone. “The only way to give them the security they need is to commit to remaining within the best trading block in the world, the single market.”

The three lawmakers are among more than 80 senior Labour figures to push for the party to set a goal for the U.K. to remain in the European Economic Area, allowing it to stay in the single market. The call, in an emailed statement on Sunday, includes 36 lawmakers and former party leader Neil Kinnock.

“Given the parliamentary arithmetic and the numbers of parliamentarians from other parties—including Conservative backbenchers—who have indicated they will join us in this endeavor, our country’s continued participation in a customs union and the single market is now in the Labour Party’s hands,” they wrote. “We must grab this chance before it is too late.”