Could Theresa May's government be found in contempt of parliament for refusing to publish the full legal advice given to the Cabinet on her Brexit deal?
A cross-party motion is before the House of Commons today triggering a debate on that question.
This is quite a moment in British political history - nothing less than one of the major branches of state - parliament - pointing the finger at the executive in the most critical and public way.
This row is about a six page legal brief which the government is doggedly refusing to publish.
- Read more: Opposition parties launch contempt of Parliament case against Government over failure to publish full Brexit legal advice
- Read more: Attorney General Geoffrey Cox accused of ‘hiding behind convention’ over Brexit legal advice
It contains the official legal advice given to the government on the Withdrawal Agreement - in particular, it is said to include revealing details about the permanency of the Irish border backstop.
MPs voted last month to force its disclosure (through an arcane procedure which ministers also tried to resist). When MPs voted, the outcome was theoretically binding on ministers.
But yesterday, the government instead gave MPs a longer explanatory document - not the raw text they had demanded.
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Attorney General Geoffrey Cox delivered a robust defence of the government's position, arguing that the secret document contains information protected by lawyer-client privilege and its contents could be used to help the EU in any future negotiations.
But it was not enough for opposition parties. Labour has tabled a motion backed by opposition parties at Westminster, including the government's own bedfellows, the DUP.
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It calls for the immediate publication of the full advice and will - if passed - find the government in contempt of Parliament for behaving in this manner.
The debate is likely to start at 12.45 and will be led by Shadow Brexit Secretary Keir Starmer.
The government has not yet said which minister will come to Parliament to defend it.
There will be a vote after a few hours of debate - MPs will be asked to pass judgement on whether ministers are in contempt. Many will relish this vote - which could be the only one of its kind in their parliamentary careers.
It's not certain what will happen if the government is found in contempt of the House. Historically, MPs found in contempt would be imprisoned by the Serjeant-at-Arms.
That won't happen now, but the normal penalties in this day and age are suspension or permanent exclusion from the House of Commons - a huge price to pay for any MP.
The likely individuals censured would be Attorney General Cox and May's de-facto deputy David Lidington.
When was an MP last found in contempt?
Sir Keir Starmer will lead the contempt debate. Image: Getty
Opposition parties clearly think the passage of the motion will be enough to force No 10 to back down and publish the advice in full.
A government minister has never been in this position in the modern history of Parliament.
The last time an MP was found in contempt was in 1947. Labour's Garry Allighan was found in contempt for accusing other MPs of selling stories to journalists - when it was actually him.
He was thrown out of the Commons and left politics completely.
There was drama - and frankly risible scenes - in the Commons last night as government whips were caught on the back foot.
Ministers desperately filibustered at the despatch box while Theresa May's parliamentary team worked out what to do.
They settled on putting an amendment on the motion, in the name of Leader of the House Andrea Leadsom.
It suggests the issue should be passed to the Privileges Committee for investigation. The seven-member cross-party committee is responsible for disciplining MPs.
This is an attempt - in classic Theresa May style, some might say - to push the debate into the long grass by setting up an investigation.
The probe would take weeks, or months, meaning the publication of the legal advice could be delayed until after the meaningful vote.
As it stands, the government is likely to lose the vote and be found in contempt. Who would have thought Brexit might lead to ministers - at least metaphorically - being locked-up?
'Throw away the key,' quipped one MP this morning.