Nat West Plonkers

I have recently returned from holiday (cycling in Denmark). On the ferry back I changed Kroners into Pounds. I am given a few fifty quid notes (I haven't seen many of these before, they are not something I encounter every day.

Monday afternoon. Nat West bank on the corner of Dover Street/Oxford Road. I have 3 fifty pound notes. Conversation with bank clerk goes roughly as follows:

Me: Oh hi, could you change these three fifty pound notes into twenties and tens?
Clerk: Do you have an account with Nat West?
Me: No, my account is with Abbey National (or Santander as they are now).
Clerk (with smug smile): Then you will have to go to Abbey National to change those.
Me (with a little sarcasm): Thank you very much.

NatWest is part of the Royal Bank of Scotland group which has recieved squillions in public money.