I’m seeing lots of UK commentary that assumes the Brexit transition period could be extended to prevent a no-deal if both sides agreed to it… but it’s really not that straightforward (thread)

The UK parliament is sovereign, so we're used to thinking 'if the government has a majority, it can legislate XYZ into existence'. But the EU is not like that: everything the EU does has to have a legal basis in its treaties

The legal basis for the Brexit transition period is that it is written into the withdrawal agreement the EU signed with the UK. This agreement was negotiated under Article 50 of the EU's founding treaty

But Article 50 can only be used to make an agreement with a departing member state, which the UK stopped being at the end of January this year. So Article 50 cannot now be used to agree a new or longer transition period

Fortunately both sides realised this and built a mechanism for extending the transition period into the withdrawal agreement... it said the transition period could be extended, but it had to be done by 30 June 2020 to give both sides time to prepare for the cliff edge.

Unfortunately, despite being knee-deep in a pandemic the UK refused to use this provision, and the deadline passed with barely a whimper. (Labour didn't even ask Boris Johnson to extend it).

So is that it...? well not exactly. Some legal 'hacks' have been proposed to extend the period. Unfortunately they all have drawbacks

One approach could be to use the EU-UK joint committee... this was set up by the withdrawal agreement and has the power to “correct errors, address omissions or other deficiencies” in the treaty. (You might know it from haggling over the Northern Ireland protocol)

But it's far from clear that changing the date the transition period ends is within the committee’s remit. You would almost certainly require a legal opinion from the European Court of Justice first. That could have been fine a couple of months ago, but it’s a bit late now

Another approach might be to simply negotiate a new treaty, using the same legal basis as is being used to negotiate the current trade agreement. Write in that treaty that there's a new transition period picking up where the old one left off at 11pm on 31 December 2020

That works in theory- but the problem is the new treaty has to be ratified. There's certainly not enough time for full ratification, and EU lawyers also think today or tomorrow is the the last realistic day you could even get provisional application done in time for 31 Dec

So it's certainly not legally straightforward to extend, and may not be possible at all to extend at this late stage. And that's setting aside the politics of whether anyone even wants an extension - neither side seem to

There's more info about the legal workarounds for extending the transition in this paper from the Institute for Government from May this year https://www.instituteforgovernment.org.uk/publications/implementing-brexit-securing-more-time