The Bank of England has announced that paper versions of the currency will expire at the end of next month, meaning they will no longer be considered legal tender.
West Bromwich West MP Shaun Bailey said the clock was now ticking for people to get rid of their paper notes.
He said: "From October, people with a UK bank account should still be able to deposit the paper notes into their bank account or at the Post Office, but spending them will be impossible.
"A lot of notes are still in circulation, so remember to spend or deposit them."
The Bank of England began the process of replacing paper £20 and £50 notes with polymer notes in February 2020.
However, it is estimated that £6billion worth of paper £50 notes remain in circulation.
It comes after the paper version of the £5 note was taken out of circulation in 2017, followed by the paper £10 note the following year.
According to the Bank of England, the new material makes notes more durable and harder to forge.
Chief cashier Sarah John, said: "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."
People are advised to get rid of old banknotes by depositing them in a bank or post office ahead of the expiry date of September 30.