So update on scottish ?......
After having spoke with an aunt of mine ( scottish....), she says nowaday there are 3 diffrent banks that can print notes in scotland........... ( dont ask, seems very complicated to me for a country less populated than the dr,.....I think....). Royal bank of Scotland, Clydsale bank ( or something to the likes of it ) and Bank of Scotland.
Scottish pounds are NOT legal tender ( term that does not apply to anything nowadays, ie credit cards, bank transfers, checks.....), not even in Scotland....... which does not make them illegal simce they are backed by the central bank of the Sterling, Bank of England.
So you should be able to change them everywhere, at the same rate as Bank of England pounds ( which is not the case ), the problem being as drsix pointed out, is that people sometimes doubt their "legality". Especially now since each denomination has 3 diffrent notes......