For the Scottish Government the European Union is like a bad penny, it just keeps turning up.

In the past week alone - no doubt exacerbated by the silly season - the issue of an independent Scotland's membership of the EU returned to haunt the SNP. All the usual questions were repeated: what does the legal advice say? Would it have to apply for membership? If accepted, on what terms, and so on (ad nauseam).

On Friday The Independent implied the First Minister had "hidden" the full legal reality behind his claim that an independent Scotland would enjoy fast-tracked membership of the EU in the 18 months between September's referendum and "independence day" in March 2016. The story hinged upon subsequent legal "clarification" (presumably from the UK Government) highlighting "serious unresolved issues" including Scottish representation in EU institutions, validity of current UK opt-outs and use of the Euro.

The same day, Italy's La Repubblica carried an interview with Catalan President Artur Mas, who apparently admitted that should the Spanish region's own (contested) independence referendum be successful next November, then between that and a "proclamation of independence" Catalonia "could remain outside of Europe". "We would need to find a transitional regime to avoid expulsion from the EU," he added. "In any case, we would ask to be readmitted."

Both stories were interesting for students of constitutional minutia (ie, me and half-a-dozen other columnists) and while not earth-shattering they did highlight interesting aspects of the SNP's thinking on Europe. Before we proceed, I happen to think it is inconceivable an independent Scotland would be "excluded" or "expelled" (insert scary word) from the EU, but then no-one - in so far as I know - has suggested it would. An awful lot of straw men have been assembled in this respect, many of them by the SNP.

But it does not necessarily follow that I also accept the Scottish Government's typically optimistic scenario about what it now calls a "seamless" process (rather than "automatic", now a banned word in the SNP lexicon). If some Unionists are guilty of scaremongering in this respect, then many Nationalists are prone to the other extreme - giving the impression membership would be a walk in a Brussels park.

Now the SNP's argument that an independent Scotland would negotiate membership from within the EU is a perfectly respectable position (albeit one dreamt up under considerable pressure in late 2012), it is just not one backed up by many independent parties. Alex Salmond and his deputy regularly wield a comment Professor James Crawford (the UK Government's own legal adviser) gave to the BBC early last year, in which he described the "Scottish estimate" of 18 months for negotiations as "realistic".

That, of course, is fair enough, and Downing Street must still be kicking itself at having sent Professor Crawford forth following publication of its first "Scotland Analysis" paper (that went into all of this at great length). But even so, Mr Salmond is a past master at the art of selective quotation, and plucking a single word - "realistic" - from Professor Crawford's interviews does not quite do him justice. Although he told the Today programme renegotiating thousands of treaties was "not going to be a major issue", he also said "membership of international organisations" would be.

That obviously included the EU, which Professor Crawford told Good Morning Scotland would "come as a matter of negotiation". In that case, he added, "there are things to negotiate, such as the British opt-outs and so on, the financial contributions, and they're not automatic." He was also quite clear that "Scotland as a new state will have to become a member of the EU by a treaty of accession". So while an 18-month time frame might be "realistic", it wouldn't necessarily be plain sailing.

On this, Professor Crawford is in agreement with the presidents of the European Commission and the European Council, but when it comes to whether an independent Scotland would constitute "a new state", the Scottish Government has not actually stated its position. The UK Government believes rUK, in line with international precedent, would be the successor state, although that might saddle it with an exclusive share of UK debt. Otherwise, this rather fundamental aspect of the indy debate has fallen by the wayside.

So it is the question of terms and conditions on which this argument turns, not the red herring of whether an independent Scotland would be in or out of Europe. Again, the Scottish Government blithely claims it would retain all extant opt-outs (a curious acknowledgement that successive UK governments have negotiated a good deal) and negotiate an exit from the Common Fisheries Policy, the latter being a point the SNP prefers to keep in the background. Equally, rUK cannot assume it would automatically retain all its current terms and conditions.

Experts, of course, are only cited when they say convenient things, and while Professor Crawford is eminent in his field, his assessment of the 18-month negotiation period as "realistic" counts for very little. Indeed, fixing a hypothetical (and much of this remains hypothetical) negotiation period so far in advance is baseless, for the actual duration depends on much beyond the control of mere politicians. Not only is a UK General Election due to take place roughly half-way through that period, but in case anyone hasn't noticed, EU negotiations - even apparently straightforward ones - tend to move extremely slowly.

As the legal advice referenced by The Independent makes clear, an independent Scotland would not be considered on a par with seven other countries waiting to join the EU. Unlike them, Scotland is already part of the union; unlike them Scotland already complies with the EU's aquis communautaire. As Nicola Sturgeon has argued, East Germany's fast-tracked membership following reunification suggests a way would be found, whatever the treaties do or do not say. In a European context, political considerations usually trump legal niceties.

But another, much wider, point is often overlooked in all of this: the SNP's view of the EU in philosophical terms. Until the late 1980s, of course, the party was rather hostile, undergoing a Damascene conversion in 1988 with the oxymoronic policy (or rather slogan) "independence in Europe". This, despite 25 years of "ever closer union", has not really been updated since, leaving the Scottish Government in the curious position of criticising the UK for being undemocratic and unequal but saying little or nothing about the EU despite both those critiques applying with bells on.

So why is one union deemed "unreformable" and the other worth attempting to improve from within (as the First Minister vaguely suggests he would try to do)? Beyond having seats at the "top table", which of course Scotland already has as part of the UK, it is a tacit acknowledgement unions can be good things. But the European Union is not a perfect organisation, something the SNP might like to acknowledge alongside critiques of the "Westminster system".