MPs have forced Theresa May to come up with a plan B on Brexit within days if her deal is defeated in parliament next week, in a further sign of growing rebellion at Westminster.
An amendment supported by a cross-party group, including nine Conservative rebels such as Dominic Grieve and Jo Johnson, was passed by 308 votes to 297 on Wednesday afternoon. It forces the British prime minister to present an alternative plan within three sitting days if the vote is lost next Tuesday.
That would accelerate the Brexit timetable, and potentially prevent Mrs May from engaging in parliamentary brinkmanship. The government’s ability to shape the Brexit process – and to ensure Mrs May’s deal is effectively the last plan standing – is now curtailed.
Under existing legislation, Mrs May would have three weeks to come up with another Brexit plan, allowing her to run down the clock to exit day and increasing the chance of a no-deal Brexit.
The vote, which came ahead of five days of parliamentary debate on Mrs May’s deal, was the latest move by MPs to assert their control over the Brexit process.
On Tuesday night, the government suffered a key defeat in the Commons, when MPs limited its ability to raise taxes in the event on a no-deal Brexit. That move, which featured 20 Tory rebels, marked the started of a parliamentary war of attrition against a no-deal Brexit.
Wednesday’s amendment was a victory for Mr Grieve, the former Conservative attorney general and a backer of a second Brexit referendum. It also worsened relations between the government and the speaker of the House of Commons, John Bercow.
Government officials had expected Mr Bercow to refuse to allow MPs to vote on Mr Grieve’s amendment to the Commons business motion, because it was “out of order”.
But the speaker, who has a history of clashes with the government and of pushing the rights of backbenchers, selected the amendment anyway. One government official complained that the speaker had acted “against the advice of his clerks”.
On Wednesday, the government also published further detail about the backstop, the controversial insurance policy designed to avoid Irish border checks. The 13-page document, intended to assuage MPs’ concerns, includes a vote for the Northern Irish assembly at Stormont before any additional EU laws can apply to Northern Ireland alone.
However, the Stormont assembly has not functioned since 2017, because of differences between the two main parties, the Democratic Unionist party and Sinn Fein.