More than £19billion worth of paper banknotes are still in circulation, ahead of a cut off date that will see them lose their legal tender status.
Paper £10 and £5 banknotes have already been withdrawn, but old style £20 and £50 notes will be redundant from September 30, under a shake-up to tackle fake money.
The Bank of England said it will continue to swap old notes for their face value, but households are being warned to use up the 775million paper notes before the autumn deadline.
There are also £105million old one pound coins in circulation, five years since losing their tender status, according to the Royal Mint.
Details of the cash still in circulation or hiding in homes was revealed in a Freedom of Information request by BBC Wales.
The round £1 coin was demonetised at midnight on 15 October 2017 and replaced by a new five-sided version that is counterfeit proof.
Of the 1.6billion that were returned to the Mint, about 1.45million were found to be counterfeits.
The old-style coin can still be deposited at high street banks - but cannot be spent in shops.
The polymer £50 note featuring the portrait of Alan Turing entered circulation on 23 June 2021, meaning the Bank's entire collection of currently-printed banknotes is made of plastic.
A spokeswoman explained that "all genuine Bank of England banknotes that have been withdrawn from circulation retain their face value for all time".
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People can also post old notes to the bank in Threadneedle Street, in the City of London, to be paid into a bank account, by cheque or, "if you live in the UK and your exchange is worth less than £50", swapped for new-style polymer ones.
If you have a UK bank account, the Bank of England said the simplest and quickest way to exchange paper £20 and £50 notes "will normally be to deposit them with your bank".
Former Bank of England governor Mark Carney – who spearheaded their introduction – said: "Polymer notes are safer than paper notes and last more than twice as long."
'Plastic' banknotes are not without issues though.
Some security features on early polymer notes, including the Queen’s face, could be rubbed off with pencil erasers, and notes can shrink to a quarter of their size if ironed while inside a pocket.
