The rare coin was found by a collector named David Crosier, who got in touch with ChangeChecker to say he had found it.
He found the 20p in his change after spending 50 years collecting coins.
Thinking the coin was plated, David sent it to The Royal Mint to be checked just in case.
The coin was examined by x-ray fluorescence spectrometry and was then confirmed to have a highly sought after minting ‘error’.
This 20p coin is shaped and stamped like a twenty pence, but is bronze like a one pence coin
So what is the error and how was it caused?
This 20p coin is shaped and stamped like a twenty pence, but is bronze like a one pence coin.
It happened after a 1p ‘blank’ found its way into the presses and a 20p was accidentally struck onto it.
Errors like this are incredibly rare – in fact ChangeChecker said they had never herd of another bronze 20p before.
Rare coin: A 20p worth £1,350 is being given away
Rare coin: The 20p is bronze, like a one pence piece, which is a very unusual error
The Royal Mint verified the authenticity of the coin with a letter.
Now ChangeChecker are giving the coin away in a specially designed presentation box alongside a Brilliant Uncirculated 1p and a Brilliant Uncirculated 20p coin from the same year.
To win the coin, entrants must register with ChangeChecker for free before Thursday 7th December.
A draw will take place on 11th December and the winner will be notified by email.
Rare coin: One lucky winner will get this presentation box with the coin and normal 20p and 1p coins
Royal Mint said of the coin: “Celebrating the 100th anniversary of the birth of Christopher Ironside, designer of the UK’s first decimal coins, this 50p features his Royal Arms design which was the runner-up to the winning design of Britannia for the first 50p in 1969.
“The Royal Arms design now appears in public for the first time some 44 years after its creation.”
Ironside, who died in 1992 aged 79, created coins for many countries.