It's after 11 p.m. in Brussels and as the summit continues, talk has turned to a hypothetical question: what happens if French President Emmanuel Macron doesn't play ball and crashes the talks?
Disclaimer: we have received no intel to suggest that this could happen. Further disclaimer: the situations below are both entirely hypothetical and, in some instances, unprecedented. That said, let's get into it.
If Macron does decide to give the UK a firm "non" to any kind of extension, then Brexit day is on April 12, which the eagle-eyed among you will note is Friday. This leaves the UK with (as far as we can work out) three options. Let's go through them in order of complexity.
No-deal Brexit: In this scenario, the clock simply runs down and the UK leaves the EU on Friday without an agreement in place. The UK will immediately be outside of single market, customs union and all the other fun EU bodies you've come to know and love over the past three years. With the least popular outcome in the House of Commons suddenly a reality, political turmoil would ensue.
May's deal's last stand: In a mad rush to avoid a no deal, Theresa May could try to reach a compromise with the Labour Party – perhaps confirmatory votes on the future relationship to get the deal approved by Friday. This would start the implementation period and the cliff edge would be avoided. With relative calm and order restored, political chaos would ensue.
Revoke article 50: This is the complicated one. The UK, as we have known since December, can unilaterally withdraw Article 50, thus ending the Brexit process for good and remaining a member state of the European Union.
But it's not that simple. The European Court of Justice said in its ruling that, while the UK can indeed revoke Article 50 unilaterally, it would have to do so in "accordance with its constitutional requirements." In the opinion of the ECJ's advocate general, the UK set a precedent of requiring parliamentary approval for Article 50. Therefore, it is is logical "that the revocation of that notification also requires parliamentary approval."
Ramming an act of parliament – or a bill – through in two days is tricky. The government could either table a bill, which requires debate and for the proposed bill to be scrutinized by parliament via a drawn out legislative process.
This can takes days, weeks or months, though as the so-called Cooper Bill to avoid no-deal Brexit proved last week, they can be forced through in a couple of days.
An easier option could be for the government to place something called a statutory instrument before the Commons. A statutory instrument is a statement of law and is generally considered to be secondary to bill. This option would be quicker, but whether it passes the ECJ test or not is a different question: the decision to trigger Article 50 was passed as a bill.
Getting all of this passed in under 48 hours would be hugely controversial and, yes, political chaos would ensue.
A final point, during the Brexit process, parliament has shown us that if it wants to do something, it usually finds a way (H/T for this observation goes to the Financial Times's political editor, George Parker).
Given that all of this is unprecedented, a bit of a mess, unlikely to happen and it's fast-approaching midnight here in Brussels, there is every chance I have got something wrong. Please feel free to correct me on Twitter, @lukemcgee.