There is no deadline to exchange old banknotes with the Bank of England. But it is usually easier and quicker to exchange notes at your own bank or at the Post Office.
How and where to safely exchange old dollars?
Exchanging old banknotes
There's NO panic to spend your old £20 and £50 banknotes
Time limit to exchange old banknotes eliminated
How to change old £5 and £10 notes for cash - with over 212million old notes still in circulation
Can you still use a ripped 5 pound note? - Quora
Old bank notes: Paper £20 and £50 paper not legal tender from
People race to exchange paper banknotes before deadline, Bank of England
Billions of pre-euro currencies still in circulation – Cash Essentials
Withdrawn banknotes