The government has got itself into a whole lot of hot water over a mere 33 paragraphs of legal advice on the Brexit “backstop” plan.

Ministers initially refused to publish the document, written by the Attorney General Geoffrey Cox to the Prime Minister last month.

Parliament passed a motion calling for any legal advice on Brexit to be published in full, but ministers failed to produce the document, issuing a “summary” of the advice instead.

Then, for the first time in the history of the House of Commons, MPs voted to hold the government in contempt of parliament for refusing to comply with their motion.

It’s a huge embarrassment for the government, so what terrible secrets lurk in the legal document they hoped would never be published in full?

What’s in the document?

Backstop

Geoffrey Cox’s note relates to the “backstop” arrangements agreed with EU negotiators.

These set out what the customs and trading arrangements will be between EU member Ireland, neighbouring Northern Ireland and the rest of the UK if no substantive UK/EU trade deal can be agreed before the end of the transition period – currently scheduled for 31 December 2020.

It’s called a “backstop” because everyone agrees that it would be better to have a proper trade deal in place with detailed arrangements.

But if no agreement can be reached, all parties said they wanted to avoid a hard border between Northern Ireland and the Republic – which risks a return to violence in the region. That’s where the backstop comes in.

Northern Ireland

The legal advice sets out in fairly stark terms that Northern Ireland would be treated differently to the rest of the UK if the backstop protocol kicked in.

Unlike the rest of the UK, Northern Ireland would remain in the EU’s single market and customs union.

Goods passing from Great Britain (England, Scotland and Wales) to Northern Ireland would be subject to a declaration process overseen by EU institutions.

Mr Cox puts it like this: “For regulatory purposes GB is essentially treated as a third country by NI.”

“Third country” is Brussels-speak for a country outside the EU. The way it’s used here could suggest that the backstop arrangement will see Northern Ireland act like an EU member state, treating Britain as a separate entity.

We already knew about a lot of this, but the language in the document has angered the DUP, the unionist party propping up Theresa May’s Conservatives in the House of Commons.

The leader of the DUP group in the Commons, Nigel Dodds, put out a statement quoting the “third country” section and adding: “This is totally unacceptable and economically mad in that it will be erecting internal economic and trade barriers within the United Kingdom.”

Ending the backstop

Mr Cox tells Mrs May that there is effectively no lawful way for the British government to pull out of the backstop arrangements unilaterally once it gets into them.

As it stands, the draft withdrawal agreement commits to finding an agreement with the EU if we want to bring the protocol to an end.

This won’t be news to regular readers. Last week FactCheck spoke to a number of academics who essentially said the same thing: a British government could theoretically end the backstop unilaterally, but only by breaking international obligations and giving the country a bad name on the world stage.

Like the law experts we spoke to, Mr Cox also says that both parties have a commitment to act in good faith, and the EU might find it legally difficult to use the withdrawal agreement to establish a permanent relationship withy Britain.

But his conclusion is the bit that Theresa May’s opponents have seized upon: “…in international law, the Protocol would endure indefinitely until a superseding agreement took its place…”

In other words, even if the EU did act in bad faith, the only legal way to end the backstop would be to come up with a new agreement.

FactCheck verdict

In view of how hard the government fought to keep this document private, we were slightly surprised at the lack of any bombshells in the Attorney General’s legal advice.

Geoffrey Cox didn’t really tell us any new facts, but he has set out some of the unpalatable elements of Theresa May’s divorce plan in phrases that have been seized on by the government’s opponents.

In fairness, we ought to say that the government set out a principled defence of why it chose not to publish the document, saying it would be a break with convention, would undermine the principle of collective decision-making by ministers, and would make it harder for legal advisers to “speak truth to power”.