Around 169 million 'round pounds' are still in circulation, the Royal Mint has confirmed. But while these coins are no longer legal tender, don't cast them aside just yet - you could trade them in or, if you're lucky, find a sought-after collector's item.
The old pound design, with a round edge, was withdrawn on 15 October 2017 and replaced with a new 12-sided coin. Yet millions of old pounds coins are still turning up in piggy banks and down the backs of sofas.
If you have a hoard of old pound coins, Which? explains how to trade them in - and how to check if they're rare or valuable.
But nine months on, the Royal Mint has confirmed that 169 million old coins have not yet been returned and are still in the public's hands. So, if you can't spend these old coins, what can you do with them?
Your best option may be to gather up all your old coins and deposit them into your bank account.
A number of banks are still accepting old £1 coins as deposits into customer accounts, according to the Royal Mint, including Bank of Scotland, Barclays, Clydesdale, Halifax, HSBC, Lloyds, Nationwide, NatWest, RBS, Santander, Ulster and Yorkshire Bank.
Customers can also deposit old coins at Post Office branches into most accounts supported by its banking services. Some banks may be willing to swap old coins for new ones, but usually, this is limited to customers (when offered at all).
, which can be returned to the Bank of England for an unlimited time period, the Royal Mint has no obligation to accept and swap old coins. Banks may also stop offering this service at some point in the future, so it pays to act now if you have a large stash.
Before you cash in your old £1 coin, it's worth taking a closer look. If you happen to have a sought-after design, it could be worth much more than it's face value.
The rarest round pound is the 2011 Edinburgh coin, which features the city's Coat of Arms and Edinburgh Castle. Just 935,000 of these were minted.
On Ebay, these coins are currently selling for between £5 and £10 in a used condition.
Other rare designs include the 2011 Cardiff £1 coin and the 2010 London £1. These three coins also have the lowest mintage figures of any £1 design. The mintage refers to the number of coins created and circulated by the Royal Mint.
Below, you can see the £1 designs with the lowest mintage figures.
But keep in mind that mintage isn't everything when determining a coin's value; age is also a factor. Older coins, even with higher mintages, are likely to be less common as many are lost or thrown away over the years.
A popular or sentimental design is likely to be hung onto by coin enthusiasts, so may be harder to find in the market.
Meanwhile, the condition is also important. Collectors are unlikely to pay a premium for a coin that has been worn, chipped or defaced, and often look for 'mint condition' items.
Also, keep an eye out for fakes or counterfeits. If you're in doubt, the Royal Mint offers a checking service.
The original round pound was first designed in 1983, making it one of the oldest British coins still in circulation last year, and the most vulnerable to counterfeiting. By 2015, one in every 30 £1 coins was a counterfeit, according to a Royal Mint report.
The new 12-sided coin design has a number of security features which make it difficult to fake, including micro-lettering around the rim, a hologram effect and additional 'hidden measures' that the Royal Mint has not revealed.
To date, there have been no reported cases of a counterfeit of the new £1 coin design, the Royal Mint has said.