Having had a few breaks in Blackpool, while found no problem with Scottish Bank Notes, in fact often got Northern Ireland notes in my change, was a bit confused when this first happened, but easily rectified, when buying my next round, just made sure the NI notes were used first.
Back in the 1950/60's as a Merchant Seaman, always made sure I had Bank of England notes when heading south, just to save any confusion. I still do when going abroad change my Scottish notes to whatever currency is used in the country I am going to, simples.