Brits are being urged to cash in their £20 and £50 paper notes which are due to expire in just four days.
Colossal queues are expected at Post Offices across the country where £1.2billion worth of old paper notes have been deposited since January.
But staff are expecting a rush of customers this week, with £6billion worth of old £20 and £8billion of old £50 notes still in circulation, according to the Bank of England.
The old paper notes will stop being legal tender after Friday when they will become worthless in shops and stores.
It leaves a small window for people to spend or deposit the cash before the notes are fully replaced with longer lasting polymer versions.
Post Office banking director Martin Kearsley reassured that most of Britain's 11,500 branches are open long hours with staff on hand to help with the process.
"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," he said.
"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."
Post Office branches are set up to handle large volumes of cash with more than £3billion in cash deposited and withdrawn every month.
So far this year, £372million worth of paper £20 banknotes and £820million worth of £50 banknotes have been deposited at Post Offices.
January saw the highest value of old notes deposited at a total value of £168.5 million, while September has seen more than £100 million worth of the notes deposited so far.
You will still be able to deposit old bank notes at the Post Office after this Friday, as well as at the Bank of England.
Some banks will also still allow you to exchange paper bank notes beyond this deadline - but do check to be sure.
Polymer £20 banknotes were first introduced in February 2020 as a more durable note with measures to avoid being copied by fraudsters.
The shinier replacement bears an image of painter J.M.W. Turner which is on display at the Tate Britain.
Meanwhile, the new £50 was released in June 2021 featuring World War Two codebreaker Alan Turin.
The scientist is best known for breaking the german Enigma code, leading to victory over Nazi Germany.
Old currency featuring the faces of Matthew Boulton, Adam Smith and James Watt will no longer be legal tender by the weekend.
However, those with a haul of paper notes still stashed away can take their cash to the bank and exchange if for new polymer notes.
Following the death of the Queen, synthetic notes will be replaced once more to allow notes with the image of King Charles to be distributed.
The new coins and notes depicting the King must first be designed before they are minted or printed and are unlikely to appear in general circulation for some time.
They will be rolled out gradually, while money with the Queen's face will remain legal tender and valid to spend until a certain date.
