I just thought to check the money brought back from our last Europe trip to be sure the UK banknotes were still good. Fortunately they are, but if your last time in the UK was prior to 2018 and you brought home some currency in anticipation of your next trip, here is where you can check to see if the notes have been withdrawn from circulation, and what to do about that:
https://www.bankofengland.co.uk/banknotes/withdrawn-banknotes
After seeing an alert about this on TripAdvisor, and checking my own supply, I remembered that I gave the last of my old pre-2018 £10 notes to some friends from England we met up in Slovenia for a rowing regatta at Lake Bled in September 2017.