You may want to find a friend coming to the UK to take them before 30th. September..or follow the advice from the Bank of England :
What to do with paper notes after 30 September
Once the 30 September 2022 deadline has passed, you will no longer be able to use Bank of England paper notes in shops, or use them to pay businesses.
After this date, many UK banks will accept withdrawn notes as deposits from customers. Some Post Offices may also accept withdrawn notes as a deposit into any bank account you can access with them.
The Bank of England will always exchange any withdrawn notes, including paper notes we have withdrawn in the past.