The notes can no longer be used in shops or to pay businesses after this week.
September 30 is the last day that the Bank of England’s paper £20 and £50 banknotes will have legal tender status.
To date, £1.2billion worth of paper £20 and £50 banknotes have been deposited at Post Office’s 11,500 branches.
The total has been made up of £372million-worth of paper £20 banknotes and £820million-worth of £50 banknotes.
The notes can no longer be used in shops or to pay businesses after this week
Joe Giddens
The Post Office is preparing for a 'last moment' rush
Rui Vieira
So far this month, over £100million-worth of the notes have been deposited at Post Office branches.
After September 30, only polymer Bank of England banknotes will have legal tender status.
The new polymer £20 notes feature artist JMW Turner, and the new polymer £50 notes feature Bletchley Park codebreaker Alan Turing.
Postmasters have their branches set up to handle large volumes of cash, with over £3billion in cash deposited and withdrawn at Post Offices every month.
Martin Kearsley, Post Office banking director, 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.
"Most Post Offices are open long hours including on Friday.”
Once the September 30 deadline passes and the Bank of England has withdrawn the legal tender status of paper £20 and £50 banknotes, people will still be able to deposit paper notes at their Post Office and many UK banks will also accept withdrawn notes as deposits from customers.