Nicola Sturgeon’s responses to Brexit have so far been adroit. But as the UK’s Brexit debate narrows its focus onto the EU’s single market, with Ms Sturgeon’s council of experts also talking of "red lines" around the single market and free movement, Scotland must avoid being boxed into a corner.

Theresa May last week said she would listen to any options Ms Sturgeon puts forward. But if Scotland chooses full access to the single market including free movement, as its preferred option for the Brexit talks, that could be very risky.

Mrs May’s opening position with Brussels, having triggered Article 50, may well be full access to the single market but with some limits on free movement. With immigration expected to fall as UK growth falters post-Brexit, what if Mrs May aimed to deliver say 80 per cent of the free movement the UK had before with the EU – could Scotland really demur, refusing to be part of the talks?

Of course, Brussels may well be much tougher than that – and put significant restrictions on UK access to the single market, especially in services, in return for less freedom of movement.

But the UK will already have lost out compared to its position in the EU today – whatever access the Tories finally negotiate, the UK will no longer have any real influence or vote on any of the single market rules. And that might soften the EU 27’s position a little.

So the UK might end up with more access to the single market and less free movement than many pundits are suggesting is likely today. And while talks continue, Mrs May will surely say it is too soon for Scotland to reject the Brexit deal as too far from its red lines. Scotland risks being boxed in at this point.

To avoid this, Scotland, in choosing its preferred EU option, must not adopt the "Little England" approach of seeing the EU as only a single market. Being a member state and having a real say and influence over all the EU’s policies – from the rules of the single market to foreign policy towards Russia or Turkey, climate change policies, asylum policy, anti-terrorism cooperation and more – is the big picture argument for staying in the EU.

Ms Sturgeon is well aware of this bigger picture – and has emphasised retaining influence and voice in the EU more than once in the weeks since the referendum.

Making the case for the big picture, strategic reasons for Scotland to stay in the EU should underpin Scotland’s preferred EU option not simply red lines on the single market and free movement, if Scotland is not to get enmeshed, by Mrs May, in the Brexit talks.

But is that tantamount to saying the only way Scotland can stay in the EU is an independent state? It might be but other options may exist.

The idea of Scotland, perhaps with Northern Ireland, and Gibraltar, staying in the EU, while the rest of the UK does not, has already been raised – some labelling it a "reverse Greenland" approach. Scottish Secretary David Mundell dismissed this idea as "fanciful" last week.

But Mr Mundell cannot stop Scotland investigating this possibility. And then Brussels may sooner than it likes – but surely not until Article 50 is triggered – comment on its feasibility. If Brussels is open to this but the UK is not, or if Brussels cannot envisage such a "reverse Greenland", then either way that will clarify Scotland’s options: Brexit with the UK or independence.

Or Scotland could – in a bold version of the full single market access and free movement option – argue for devolution of migration policy, participating fully in free movement and the single market, while the rest of the UK went for a Canada trade-deal approach. This need not mean a border between Scotland and England but Mrs May might well think it did.

Yet such an intermediate route for Scotland’s preferred EU option would still risk tangling Scotland up in two years or more of the UK’s Brexit talks, waiting to see the outcome for the UK as a whole on the single market and free movement. Mrs May would be only too happy at that while Ms Sturgeon will surely do her best to avoid it.

The UK’s negotiating stance needs to be ready soon. Whether Ms Sturgeon rebuffs or accepts that stance – and whether Scotland gets entangled in the Brexit talks or not – will soon make clear whether Scotland is on the path to a rapid second independence referendum or not.

Kirsty Hughes is an Associate Fellow of Friends of Europe.