Brexit bill vote: How important is tonight's clash on the EU withdrawal legislation?

What is the EU Withdrawal Bill?

It is the key Brexit legislation – pasting 40 years of EU legislation onto the UK statute book in time for our exit in March 2019, before the Government decides later which bits should be retained or removed.

Why is passing it so important for Theresa May?

Legally it is crucial – because the law must be ready for Brexit day, to provide certainty. But getting the Bill through Parliament without being forced to retreat is also vital to her political standing, both at home and abroad.

Why are Tory MPs are threatening to vote against the Government?

The Prime Minister has conceded to MPs a vote, and an amendable Bill, on the final Brexit deal – but has insisted it will be a “take it or leave it” offer, meaning the UK would crash out of the EU without a deal in March 2019, if hers is rejected.

Tonight’s showdown is designed to ensure it is a “meaningful vote” by giving MPs a veto over the terms of withdrawal – and the potential to delay it, if no satisfactory deal is reached.

Who else is planning to vote against the Government?

All the Opposition parties are expected to vote with the Tory rebels. Labour’s Keir Starmer said Parliament must be given “a proper say on the Brexit deal” – adding: “The terms of our future are not for the Government alone to determine.”

How likely is a Government defeat?

Ten Conservative MPs, led by former Attorney General Dominic Grieve, have signed the amendment – including former Cabinet ministers Ken Clarke and Nicky Morgan. At least another 10 are thought to be sympathetic.

Given that the Prime Minister’s working majority is only 13, she will lose - if those rebels stand firm, amid heavy arm-twisting from Tory whips not to give her “a bloody nose”.

What is the key amendment proposed by the Tory rebels?

Amendment 7. It would prevent the Government using so-called “Henry VIII powers” to enact withdrawal, bypassing MPs even if they reject the deal the Prime Minister secures.

It would override clause 9 in the EU Withdrawal Bill, stopping that enactment until Parliament has voted in favour of a separate Bill, which could be amended, perhaps to keep the UK in the EU single market and customs union.

What would happen if the Government is defeated?

Parliament would have a truly “meaningful vote” – with the potential to send Ms May back to Brussels to seek a better agreement, if hers is rejected. However, the other EU countries would need to agree to this.

How could the EU Summit and future Brexit talks be affected?

The timing could not be worse for the Prime Minister, a day before the 27 EU heads of government are expected to agree “sufficient progress” has been made to move the Brexit talks onto the transitional deal she seeks.

Defeat tonight would raise fresh fears in EU capitals that she lacks the muscle to deliver on her Brexit promises. For that reason, Ms May could choose to accept the amendment at the death tonight, rather than lose the vote.