Today is the last day you can spend your old £20 and £50 paper banknotes.
The Bank of England is withdrawing the legal tender status of the two notes after today, September, 30.
It means any old paper notes you have saved at home will be worthless in shops from tomorrow and you will have to deposit them.
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People can still deposit both bank notes at the Bank of England or into their accounts through a Post Office.
Any new bank notes made from polymer displaying the portrait of Queen Elizabeth II will remain legal tender and people can still use them in shops following her death.
The Bank of England estimates there are still more than 250 million individual £20 banknotes and more than 110 million £50 banknotes. This means there are still billions of pounds worth of old legal tender still in circulation.
Post Offices across the city are expecting long queues today as it is estimated around £1.2billion worth of old paper notes have been deposited since January.
The Post Office banking director Martin Kearsley has reassured the country that most of Britain's 11,500 branches will be open for longer hours with staff there to help people deposit any cash they have.
Martin said: "We're fully aware that people lead busy lives and some may put off depositing their paper £20 and £50 banknotes until the last moment.
"Postmasters and their staff are on hand to provide that human reassurance that your old notes have been deposited into your bank account and will provide a receipt too."
January saw the highest value of the paper notes deposited at a value of around £168 million. September has seen more than £100 million worth of notes deposited so far.
Follow Queen Elizabeth's death the polymer notes will be replaced again by notes featuring King Charles' portrait, but this is not expected to be until next year.
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