There seems to be some ongoing debate as to whether or not Scottish notes are fully legal currency in England. As far as I have always been aware, the fact that they say £10 sterling (or whatever) makes them legal throughout the UK. Certainly its a long time since anyone ever refused to take mine off me in England - tho' Sam Smiths pubs are intructed not to accept anything above a £5 note, and there are some concerns about the number of forgeries of Scottish £20s - hopefully improved by the new issue. If in doubt, any bank will exchange them for the local version.
Now if you do want to confuse an English shopkeeper, try paying with an Ulster banknote!!
Anthony