I don’t like them either and find them awkward to fold, to fit into a small purse.
Regarding the paper £20 notes - the BBC was reporting yesterday that there is currently no deadline for their withdrawal, they will simply be removed from circulation, gradually. Though the expectation is that a six month notice period would be applied before any final withdrawal.
They also reported that millions of pounds worth of paper £10 and £5 notes have never been surrendered! So large quantities of those are still in existence somewhere.
Apparently if you have old £5 or £10 notes, the Bank of England will still exchange them for legal tender.
(I wish I had a forgotten box full tucked away ...) ??