Nicola Sturgeon has pre-empted Theresa May’s triggering of Article 50, getting in first with her plan to hold a second independence referendum after Brexit plans are clearer and before (or very close to the moment when) the UK leaves the EU.

But if May triggers Article 50 this month, as planned, then the UK will leave the EU by March 2019 (given Article 50’s two year deadline).  So if there is an independence referendum in autumn 2018 or spring 2019, Scotland will still be part of the UK when it leaves the EU in March 2019, even if Scotland has voted ‘yes’ to independence. There is no way out of Brexit in the short-term it seems.

So does Nicola Sturgeon’s timing make sense? Broadly, the answer is yes. By autumn 2018, there will either be a UK-EU27 exit deal, which will also set out goals for a future UK-EU27 trade deal, or negotiations will have broken down and the UK will be heading for the EU exit door without a deal (unless a talks breakdown leads to a complete rethink of Brexit after all). So the context for a second Scottish independence referendum should be clear.

But, unlike in 2014, in the event of a ‘yes’ vote in a second independence referendum, the rest of the UK will not stay in the EU or in its single market. So if, at the fastest, Scotland could separate from the rest of the UK (rUK) in 18 months, legally there appears to be no way that Scotland can avoid leaving the EU with rUK in March 2019. And it couldn’t start formal talks with Brussels to re-join the EU until it was independent – possibly in 2020.

But imagine the scenario in late autumn 2018, if Scotland has voted yes to independence in the EU. There is then little point in Scotland repealing all its EU laws and leaving all EU agencies, research programmes, regional and agricultural policies and more, just to re-join them several years later.

Nor would it be in rUK’s interest for Scotland to first unwind EU laws, along with rUK, only to reinstate them over the next three to four years during its accession process. Scotland and rUK, in the face of an independence vote, will need to agree a separation deal.

There is no point in negotiating that separation deal twice – once under the conditions of Scotland being outside the EU, like rUK, and then again once Scotland has re-joined the EU. How to handle trade, borders, free movement of people and more, will depend on Scotland’s future status in the EU.

So if Scotland were to leave the EU with the rest of the UK in March 2019, is there any way to avoid this messy outcome of firstly negotiating a divorce deal with rUK outside the EU, and then negotiating a second new relationship (based on the UK’s future UK-EU27 deal) once Scotland is back inside?

This will depend on three-way talks between London, Brussels and Edinburgh. The real challenge would be not whether Scotland can get some sort of ‘special status’ keeping it within the EU but whether and how Scotland can pragmatically stay aligned with EU laws and policies, and within its regulatory programmes and networks.

If Scotland goes through a ‘normal’ EU accession process, then this challenge – of staying aligned to EU laws – will need to be met firstly while Scotland is still part of the UK and outside the EU, and secondly while it is independent and outside the EU. The latter part is relatively straightforward – the EU is very experienced in ensuring countries outside the EU align with its laws and policies before actually joining. So the real challenge will be for the period of time when Scotland is outside the EU and part of the UK.

Ironically, the best way to handle Scotland staying aligned with EU laws while still in the UK – after a ‘yes’ vote in an autumn 2018 referendum – would be to draw on the proposals from the Scottish government’s compromise document “Scotland’s place in Europe’. These outline how Scotland could stay in the UK and in the EU’s single market. There will need to be more rapid policy thinking to see how Scotland could stay in all other EU policies too, for the transition phase while it would be in the UK and outside the EU – but that is surely not beyond policy-makers in Edinburgh, London and Brussels to figure out.