Despite Scotland being considered as part of the United Kingdom, they print their own currency which issued by the Bank of Scotland (but the confusing part is that there’s no separate currency code for Scottish Pounds) and the fact it is “legal currency” but not officially legal tender (even in Scotland itself), it’s weird.

I would say that using GBP is better than Scottish Pound to not confuse cashiers since it’s up to their discretion whether they’ll accept Scottish money in Britain & vice versa. I’ve heard most will refuse Scottish Pound due to unfamiliarity, even worse there are three banks printing their own version of Scottish Pounds.