Prime Minister Theresa May suggested yesterday that MPs may get to decide whether Britain eventually joins the “backstop” plan to avoid post-Brexit border checks with Ireland. May told BBC Radio that she was looking at allowing lawmakers a vote on the arrangement, which would keep the country in a customs union with the European Union after the end of the proposed Brexit transition period in December 2020.

The alternative, according to the deal struck between May and the EU, would be to extend the transition period for up to two years, during which time Britain would largely enjoy the same relationship with the bloc, despite officially leaving on March 29, 2019.

“We’re looking at is this question around the backstop and the role of parliament,” May said. “The backstop is talked about as if it’s automatic. Actually it’s not automatic. There is a choice.

“The question is do we go into the backstop, do we extend... the transition period? I’m exploring.”

May is drumming up support for her deal, but faces daunting odds with scores of her own MPs set to vote against the government on December 11.

The Conservative prime minister commands a slim working majority in parliament thanks to a deal with Northern Ireland’s DUP, which is fiercely opposed to her plan.

DUP leader Nigel Dodds said his party would vote against the deal, but would not move to bring down May’s government.

“If it (the deal) is defeated, it would be somewhat illogical—having achieved our aim trying to get to a better deal—it would be illogical then to turn around the next day and say ‘let’s vote the government out’,” he told ITV.

“I think then we start on a process to try to get a better deal,” he added.

The backstop issue is the key sticking point, with official legal advice suggesting Britain could get indefinitely stuck in a customs arrangement, having no power to unilaterally withdraw.

According to media reports, May’s office has attempted to win over rebellious backbenchers by suggesting that MPs may even be able to vote on rejecting both options of the deal, but was rebuffed by leading Brexiteers.

Conservative MP Jacob Rees-Mogg, leader of the influential eurosceptic ERG group, told the Daily Mail that such a proposal would mean ripping up the Withdrawal Agreement and renegotiating it entirely, something the EU has ruled out.

MPs were to hold a third day of debates on the deal on Thursday, focusing on its economic impacts.