That means there are just 100 days left before the notes are no longer legal tender. The old money has been replaced with longer-lasting polymer notes.
The BOE estimates there are more than £6 billion worth of paper £20 notes tucked away in wallets, piggy banks and old trouser pockets.
Additionally, they estimate there are £8 billion worth of old £50 notes in circulation, reports The Mirror.
It is a year since the Bank first issued the polymer £50 banknote featuring Bletchley Park codebreaker and scientist Alan Turing to complete the revamp of £5, £10, £20 and £50 notes.
His image replaced entrepreneur Matthew Boulton and engineer James Watt while the new £20 featuring artist JMW Turner replaced economist Adam Smith in 2020.
Both paper notes will no longer be legal tender on September 30, the Bank of England said. After this date, you will not be able to spend them in stores.
The BOE is encouraging anyone who still has these to use them or deposit them at their bank or a Post Office during these last 100 days.
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 swapped for new-style polymer ones if you have less than £50 to exchange.
Its chief cashier Sarah John said: “Changing our banknotes from paper to polymer over recent years has been an important development, because it makes them more difficult to counterfeit, and means they are more durable.
“The majority of paper banknotes have now been taken out of circulation, but a significant number remain in the economy, so we’re asking you to check if you have any at home.
“For the next 100 days, these can still be used or deposited at your bank in the normal way.”
It is believed that more than 300 million individual £20 banknotes, and 160 million paper £50 banknotes are still in circulation.
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.”
The polymer banknotes are not without issues though.
Some notes can accidentally shrink to a quarter of their size if ironed while inside a pocket.