Theresa May has been forced to hand MPs control of Brexit after the government lost a key battle in the Commons on Tuesday. 

In a pivotal moment in the Brexit saga, MPs inflicted defeat on the government by throwing their weight behind a motion by Dominic Grieve.

It means that, should May’s Brexit plan be voted down next week – as is widely anticipated – MPs can effectively instruct minsters on what to do next and amend her “plan B” option.  

The government lost by a sizeable 22 votes – 321 to 299 – just minutes after MPs voted to find ministers in contempt of parliament over their refusal to publish secret Brexit legal advice. 

The amendment move opens the door for MPs to back alternatives to May’s Brexit, including a Norway-style Brexit, a re-run of the referendum, or a Canada-style deal. 

As well as potentially tying May’s hands, it drastically reduces the prospect of the UK crashing out with no deal at all, given that a clear majority of MPs believe it would be catastrophic for the economy.  

Significantly, Grieve’s motion was backed by Tory MPs Nick Boles, Oliver Letwin and George Freeman who have backed a deal close to EEA or EFTA membership. 

Grieve told MPs that it was “contrary to all sensible practices and I have to say slightly disrespectful of this House” that May’s plan B could not be amended by MPs, who were “fully focused on resolving outstanding issues” with Brexit. 

In an important development, Tory MP Sir Oliver Letwin, who will vote for May’s deal, said he would back a Norway-style deal as the “next best step” should the government be defeated next week. 

Labour MP Hilary Benn, the chair of the Commons Brexit select committee, told the House his party would back the amendment and had some scathing words for the government. 

He said: This whole process unfortunately has shown the government’s marked reluctance to listen to the House, to trust the House and share information with the House.

“I suspect what the government has sown it will reap in the vote next Tuesday.” 

What happens now? 

Parliament will vote on May’s Brexit plan – the EU Withdrawal Agreement and political declaration setting out a framework for a future relationship – on Tuesday December 11. 

Once the deal is voted down, the prime minister has 21 days to renegotiate with the EU and return to parliament with a motion. 

Grieve’s amendment means MPs can now amend that motion. 

Brexiteers argued that the government – also known as the executive – could ignore such a motion and that the final vote on the legislation is all that counts. 

But such a strategy looks untenable for Theresa May. The vote comes just hours after extraordinary scenes in the Commons as MPs found the government in contempt of parliament over its refusal to share legal advice given to ministers about the Brexit deal. 

Remain campaigners will also be rejoicing as the developments come hot on the heels of a senior law officer at the European Court of Justice, Campos Sánchez-Bordona, said that he believed the UK had the right to unilaterally revoke Article 50.