Since Brexit fundamentally alters the terms on which Scotland voted to remain part of the UK in 2014, Nicola Sturgeon is perfectly within her rights to demand a second referendum on whatever timetable the Scottish parliament decides. It was, after all, the Better Together campaign that chose to make Scotland’s place in the EU one of the three big issues of the last referendum campaign, along with public spending and the economy. Scottish voters were warned that independence would leave them locked out of the EU. Now independence is their only hope of avoiding that fate. Unionists have a job on their hands to explain why that no longer matters.

The context of EU withdrawal means that the second referendum, when it comes, will not be a simple re-run of the first. The issues and arguments will be different, as will the electoral coalitions that line up behind them. Whether this favours a different outcome remains to be seen. Much will depend on how difficult and painful the process of Brexit turns out to be, and how long Theresa May is able to postpone the day of reckoning. Yet there are already at least four significant respects in which Brexit has overturned the assumptions of three years ago.

1. Better together... with what?

The first goes to heart of the message unionists rallied behind in 2014 – Better Together. At that time, the ability to be Scottish, British and European appealed to many voters as the best of all possible worlds. Brexit now means that Scots will be forced to choose between being British or European, raising the obvious question: Better Together with whom? If the ethic of togetherness is the supreme political virtue, it is no longer obvious that staying in the UK is the best way to express it. Giving priority to Scotland’s union with Europe might also be thought of as a valid unionist position, especially if the term is used in its broadest sense. This means that independence cannot any more be dismissed as an exclusively nationalist cause. It has arguably become the logical internationalist position as well.

The number of people open to this line of reasoning is potentially big enough to sway the result in a tight race. Consider Edinburgh, which recorded the biggest Remain vote in the Scotland last year and one of the largest No votes two years earlier. A lot depends on whether this swing group of "unionists for independence" is cancelled out by the emergence of another new group – "nationalists for the union". It is often forgotten that withdrawal from the Common Market was the default position of the SNP until 1988. Around a third of the party’s supporters voted Leave last year, including its former deputy leader, Jim Sillars, who has threatened to boycott Indyref 2 if independence means re-joining the EU. The polling averages suggest that the numbers have barely changed since 2014, but there is a lot going on below the surface.

Read more: Who would oppose Scottish independence in a second referendum campaign?

2. EU membership is in reach

The second big difference is that Brexit clears the path for an independent Scotland to join EU. Three years ago, there were good reasons for expecting significant obstacles to early entry; something that No campaigners took every opportunity to highlight. Both the common European interest and the interests of several large member states meant that Brussels had a strong reason to punish secessionism. The UK, Spain, Italy and even France were nervous about establishing a precedent that might galvanise separatist movements elsewhere. Scotland would therefore have to serve its time on the naughty step.

Thanks to Brexit, the EU is no longer obliged to take the UK’s interests into account and the overriding concern is with the possible fragmentation of the EU itself rather than its constituent parts. Scotland’s desire to join would now be welcomed and rewarded. The main sticking point would still be Spain, currently dealing with its own separatist challenge. Yet even this may be less of a problem than it seems. Faced with overwhelming pressure from its EU partners, Spain would probably drop its veto in exchange for a political declaration making it clear that territories seceding from existing member states could expect to be treated very differently. Prior to Brexit, it was likely that an independent Scotland would have been shut out of the EU for a decade or more. Now it could realistically aspire to full membership within about three years.

Read more: Independent Scotland would have "zero technical problems" rejoining EU

3. Scotland can think big

A third consequence of Brexit is that it transforms the debate about Scotland’s economic future. The conventional view that the decline in oil revenues has made independence unaffordable seems oddly myopic at a time when trade relations are being thrown into a state of flux. The UK has for many years been the EU’s top destination for foreign direct investment thanks to a unique combination of advantages, such as the English language, a high quality of life, barrier-free trade with the single market and unimpeded access to the European labour pool. Hard Brexit means that two of these advantages are about to be forfeited. The short-term beneficiary of this may turn out to be the Republic of Ireland, but there is no reason why an independent Scotland couldn’t lay claim to the UK’s role as a magnet for inward investment by guaranteeing continuity in terms of market access.

The counter argument is that Scotland’s trade with the rest of the UK is four times larger than its trade with the rest of the EU. That is true as a statement of the current position, but any assessment of future potential would acknowledge that the EU remains ten times larger than the UK. Scotland faces major economic adjustments whether it stays in the UK or not. So why not think big and adjust to the needs of a larger market? It could even be argued that independence in Europe offers Scotland its best opportunity to break free of an economic model that has become heavily dependent to two finite assets; North Sea oil and English good will. It is certainly more plausible and inspiring than arguments based on the assumption that business as usual is an option.

Read more: Brexit makes Scottish independence economically more attractive

4. There is no status quo

Finally, we can see that Brexit has overturned the calculus of risk that played such an important role in the last referendum debate. Scotland can’t opt for the status quo this time because there is no status quo. We have no idea what the UK’s future trading relationships are going to look like or how this will impact on our prosperity. Nor is there any certainty about public spending. Scotland currently benefits from a UK fiscal transfer, but even this must be in doubt given the tide of resentful English nationalism that has swept the country and shows no sign of ebbing? What we do know is that the Conservatives have threatened to turn the UK into a low regulation, offshore tax haven unless the EU gives them what they want. We also know that there is no one there to stop them since Labour doesn’t look like it will be in a position to win an election until 2030 at the earliest. This time, Project Fear cuts both ways.

Read more: We need a new constitutional settlement - and not just for the Scots

Brexit is already a game changer. The only question is whether it will prove to be a result changer. So far the debate has evolved in ways that help those arguing for independence, but that won’t necessarily remain the case. The issue of timing has become important precisely because the Prime Minister hopes to restore a favourable balance of risk by allowing time for Brexit to become normalised. For that to become possible, she will first have to return from Brussels with a better deal than currently looks achievable.