The Bank Of England has issued a warning to those with paper £20 and £50 notes to use them before they go out of circulation.
On 30 September, paper notes are set to be replaced with ones made from polymer, a thin, flexible plastic, similar to the £5 and £10 notes that are in circulation now.
The new material is not only more durable but harder to counterfeit.
Come the September deadline, which is only 100 days away, paper £20 and £50 notes can no longer be spent in shops, but they can be deposited by anyone with a UK bank account.
The Bank of England’s chief cashier, Sarah John, explained: "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."
The paper notes issued by Bank of Scotland, Clydesdale Bank and Royal Bank of Scotland will also go out of circulation after 30 September, as will £20 and £50 notes from AIB Group, Danske Bank, Ulster Bank in Northern Ireland and Bank of Ireland.
There’s an estimated 163 million paper £50 banknotes still in circulation and 314 million £20 paper notes, the BBC reports.
Not only are the new notes made from a more durable polymer, but The Bank of England claims that they are more environmentally friendly thanks to their longer lifespan, which The Carbon Trust has confirmed.
Polymer bank notes are also designed in a way that allows blind and partially sighted people to identify them.
They write: "The new polymer notes allow for enhanced security features, such as the see-through window and holograms. This makes them harder to counterfeit than paper notes.
"They’re stronger, too: a polymer fiver is expected to last two-and-a-half times longer than the old paper £5 note. Although, while our notes are stronger, they are not indestructible – so you should still take care of them."
Interestingly, the new polymer notes will see JMW Turner on the £20 note and Alan Turing on the £50 note, replacing Adam Smith and James Watt on the paper versions.