About £40bn-worth of paper banknotes, which will be replaced by new polymer £20, are set to be turned into compost.
The Bank of England will withdraw and recycle the old notes “to use as soil improver for agriculture”, according to the BBC.
This will mark the biggest replacement of banknotes in UK history.
Businesses and banks will return notes to one of the Note Circulation Scheme (NCS) members — G4S Cash Solutions, the Post Office, National Westminster Bank or Vaultex UK.
Mark Saunders at G4S, which handles two thirds of Britain's banknotes, said: "It's an enormous operation the general public will barely notice.”
The Bank of England will give an official six-month warning before taking the old notes, featuring noted economist Adam Smith, out of circulation.
The new £20 note featuring artist JWM Turner entered circulation on Thursday. Both notes will be accepted as legal tender until that time when the old one is withdrawn and destroyed.
The Bank of England said: "You will still be able to use the paper £20 note until we withdraw it from circulation. We will announce the withdrawal date after we have issued our new polymer £20 note. We will give six months' notice of this withdrawal date."
The Bank is calling the new polymer note “the most secure bank note yet”. It features two security windows and a two-colour foil to thwart fraudsters, as well as a “tactile feature” to help vision-impaired people identify it.
It follows the release of the polymer Winston Churchill £5 and Jane Austen £10. A new £50 note bearing the likeness of mathematician and computer scientist Alan Turing will be released by the end of 2021.
The £20 note was last replaced in 2007, when the Adam Smith note replaced the Edward Elgar note that had been in circulation since 1999. It took three years for the note to be withdrawn entirely.
BBC News said it is likely to be 2021 at the earliest before the Bank sends out its six-month deadline for the paper Adam Smith £20.
Tens of thousands of ATMs across the UK will have to be replaced or reconfigured to accommodate the news notes, which are 15% smaller than the old ones.
“The life of a note is extraordinary. After we’ve machine sorted the cotton notes out, they’ll be parcelled, weighed and sealed — in cages in our vaults before being securely transported back to the Bank of England for verification and destruction,” Saunders said.
He added: “It’s an enormous operation the general public will barely notice, and that’s the way we want it.”
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