//That said, the Scottish Independence referendum took place before Brexit was more than a twinkle in Nigel’s eye,...//
No it didn't Naomi.
By 2012 there was growing unease at the UK's continued EU membership. As I've previously pointed out, as early as January 2013, Mr Cameron (under pressure from the rising popularity of UKIP and a sizeable chunk of his own party) promised that, should the Conservatives win the 2015 General Election, he would renegotiate the UK's relationship with the EU and call a referendum based on the new terms.
So when they voted in September 2014 it should have been clear to the Scots that there was a possibility that the UK would leave the EU. If they didn't take that possibility into account they should have; if they took it into account but dismissed it as to be so unlikely as not to be worth worrying about they were wrong. Either way, they had fair warning. There was obviously far more to keep them in the UK than the threat of the UK leaving the EU would persuade them to leave.
I don't particularly care whether Scotland holds another referendum or, if they do, what the result is. But to ride on the back of what they say is a material difference is disingenuous as they should have taken the likelihood of such a change into account. They can't really expect a fresh referendum every time the UK (of which they voted to remain part of) takes a decision with which some of them do not agree.