Consumers are being encouraged to spend, bank or donate old pound coins as the deadline for using them looms.
Shops have been told not to accept the old £1 coin from 15 October as it will no longer be legal tender, although banks and Post Offices will still accept the coins for a limited time.
Businesses are also being reminded to get ready by updating equipment such as payment machines and informing customers.
The Treasury says there are now more new 12-sided pound coins in circulation than old round pounds.
Andrew Jones MP, the exchequer secretary to the Treasury, said: “To have more new coins in circulation than old at this point is great news. “However, with less than 100 days to go, the clock is ticking.
“We are urging the public to spend, bank or donate their old pound coins and asking businesses who are yet to do so, to update their systems before the old coin ceases to be legal tender.”
The new coin was launched on 28 March 2017 and is described by the Royal Mint as being the most secure coin in the world.
Security features include a latent image that acts like a hologram changing from a ‘£’ symbol to the number ‘1’ when the coin is seen from different angles.
It also has tiny lettering on the lower inside rim on both sides of the coin, milled edges and a “hidden security feature” built into the coin to protect it from counterfeiting.
The old pound coin is being replaced because of its vulnerability to counterfeiters – about one in 30 of the old £1 in circulation is a fake.
Adam Lawrence, chief executive and deputy master of the Royal Mint, said: “The Royal Mint is very proud to have delivered the new 12-sided £1 pound coin and ensuring a smooth transition is now our top priority.
“The new 12-sided £1 coin was brought in to tackle the rise of counterfeit coins, which cost businesses and the taxpayers across the UK millions of pounds every year.
“With less than three months to go before the round pound loses legal tender status, it is vital that the public continue to return their old pound coins.”