Old bank notes should be acceptable to be paid into a bank account, whether its a business or personal account. I've paid in old bank notes into a business account in the last year, no questions were asked.
The bank would prefer any odd notes are not bundled with the main takings, so old BOE and Scottish/Irish notes should be put in a separate bundle.


Aside from the possibility of being able to feed them into automated checkouts or ticketing machines, your best bet CHSBoater might be If you can befriend a local resident during your stay who has a bank account and ask them to swap them for you.
A money exchanger in the UK might also take pity on you but would probably charge you for the convenience if they did.