Theresa May has lost a historic vote after MPs ruled that the Government was in contempt of Parliament over its refusal to publish its own Brexit legal advice.

This is the first time the Commons has found a Government to be in contempt.

The Prime Minister was defeated by 311 votes to 293 – a defeat that sets a worrying precedent for Mrs May’s ability to get legislation through.

MPs decided the Prime Minister failed to comply with a binding Commons vote that required the government to publish attorney general Geoffrey Cox’s full legal document on Theresa May’s Brexit deal.

Shadow Brexit secretary Sir Keir Starmer said that the finding of contempt was “a badge of shame” for the Government, with “huge constitutional and political significance”.

The vote demands the “final and full” legal advice on the Brexit deal. Commons leader Andrea Leadsom said that the Government would respond to the vote tomorrow.

Brexiteers believe the legal text will make it clear that the UK would not be able to terminate the backstop arrangement without the EU’s permission if it were triggered, possibly trapping Britain in a Customs Union permanently.

The result came just minutes before the beginning of five days of debate on the deal the Prime Minister agreed with the EU before MPs’ ‘meaningful vote’ on the issue.

Mr Cox released a summary of the advice yesterday, arguing that releasing the full document would not be in the public interest.

It comes as the European Court of Justice found that Britain can reverse Article 50 and cancel Brexit without the permission of Europe.

Speaker John Bercow gave the green light to a debate and vote on the motion of contempt after a demand from the six opposition parties.

Mr Cox responded by insisting the Government has ‘gone out of its way’ to satisfy Parliament’s motion calling for the release of the full legal advice.

He said the wording of Sir Keir Starmer’s motion was ‘extremely vague’ and did not compel him to publish the advice in full.

He added: “Unless there is clarity on these questions it is simply not possible for the Government to know how to comply with the motion.

“It is particularly important that if anyone is to face sanctions for contempt he or she should fairly know how to comply with it.”