Royal Mint
The new pound coin.
Chief Secretary to the Treasury David Gauke announced on Sunday that the new 12-sided pound coin will enter circulation 28 March 2017, meaning existing versions of the coin will become worthless on 15 October.
The government estimates that £1.3 billion ($1.6 billion) worth of coins are stashed away in home piggy banks, around a third - or £433 million - of which are pound coins. These will have to be spent or returned to the bank before they expire as legal tender by the October deadline.
Gauke said: "Our message is clear: If you have a round one pound coin sitting at home or in your wallet, you need to spend it or return it to your bank before 15 October."
The new pound coin was unveiled in March 2016 and former Chancellor George Osborne described it as the "most secure circulating coin anywhere in the world." It is 12-sided and has a hologram-like image under the Queen's head which changes from a '£' symbol to the number '1' at different angles.
More than 1.5 billion new pound coins will be produced by the Royal Mint in Llantrisant, Wales, at a rate of up to 2,000 a minute. Some of the round pound coins returned by the public will be melted down and reused to make the new pound coin.
"This is a historic moment as it's the first time we've introduced a new £1 coin since 1983, and this one will be harder to counterfeit than ever before," Gauke said.