At my workplace we are told to call the supervisor to check all Scottish notes. One customer kicked off at a colleague, arguing that he was in a hurry and she was wasting time by calling a manager, and in any case she had to accept it because it was legal tender. After some debate with the supervisor he was refused service and was asked to leave without his purchases.
About a month later the same guy ended up at my till and handed me a Scottish note, I said “one moment please sir” and rang the bell, he then made a play of rifling through his wallet before saying “it’s okay mate, give me that back and take this one”, and handing me an English note…..
I once ended up with an Ulster Bank note after a visit to Liverpool, the supermarket cashier back in London didn’t want to accept it, I didn’t bother arguing and just used it in the self scan on my next visit a couple of days later.