Next month sees the launch of the new 12-sided £1 coin, and Brits have until October 15 to use up any current coins they have lying around - before they become worthless later this year.

But, if you've a handful of 'round pounds' tucked away in savings, you may be better off keeping keeping them in your collection, as according to the money specialists at changechecker.org, you could be sitting on a small fortune.

In a new 'Scarcity Index', CoinChecker has identified 24 of the rarest £1 coins to have ever circulated the UK - with some worth as much as £50 each.

In the report, the blog revealed the coins that are worth £25 or more - with the value likely to rise as the current round pounds lose their status on October 15, 2017.

The rarest coin on the index, known as the Edinburgh City 2011 £1 coin, is selling for as much as £34, which is more than thirty times its value.

While the 2011 Cardiff City £1 coin has sold for £20 and the London City 2010 coin is selling for £10.

Test versions, known as "proof coins" are even more valuable with collectors.

These are made by The Royal Mint and are struck at a lower speed with a higher finish. Check your £1 coins before you hand them in.

The rarest £1 coins to watch for in order (by design)

Scotland: Edinburgh City (2011)

Edinburgh City
Edinburgh City

Wales: Cardiff City (2011)

Cardiff City
Cardiff City

England: London City (2010)

London
London

Scotland: Thistle & Bluebell (2014)

Thistle & Bluebell
Thistle & Bluebell

UK: Crowned Shield (1988)

Crowned Shield
Crowned Shield

N.I.: Flax & Shamrock: (2014)

Flax & Shamrock
Flax & Shamrock

Wales: Daffodil & Leek (2013)

Daffodil & Leek
Daffodil & Leek

Scotland: Lion Rampant (1994)

Lion Rampant
Lion Rampant

England: Millennium Bridge (2007)

Millennium Bridge
Millennium Bridge

N.I.: Flax: (1986, 1991)

N.I.: Egyptian Arch Railway Bridge (2006)

England: Oak Tree (1987, 1992)

Scotland: Forth Railway Bridge (2004)

Wales: Dragon Passant (1995, 2000)

Wales: Menai Bridge (2005)

N.I.: Celtic Cross (1996, 2001)

UK: Royal Arms (1983, 1993, 2003, 2008)

Scotland: Thistle (1984, 1989)

Wales: Leek (1985, 1990)

England: Three Lions (1997, 2002)

UK: Royal Arms Shield (2008 - 2015)

UK: Royal Coat of Arms (2015)

The history behind the current 'round pound'

Replacing £1 notes, £1 coins were first launched on 21 April, 1983. Since then, a total of 2.2 billion £1 coins have been struck for circulation - but not all are still in use.

The last available figures for coins in circulation, published by The Royal Mint in 2014, suggest that 1,553,000,000 £1 coins are still in use today.

But, an estimated 650 million have been withdrawn, mostly due to damage over the years with many classed as 'worn out'.

As a result, certain editions are now classed as 'rare' and collectors are willing to cough up high amounts for them.

Valuable £1 coins
Valuable £1 coins

A spokesperson from ChangeChecker.org said: "£1 coins will be getting rarer by the day as they start to be removed from circulation once the new 12-sided coin is released on 28 March.

"And, come 15 October, one thing is for certain, any collector looking to own a £1 coin collection will be paying a premium.

"So don't just spend your £1 coins. Check them. Rather than being worthless come 15 October, they may have even more value to collectors – especially if you own a particularly scarce £1 coin."

If you've got a stash of coins packed away - it's time to crack open your piggy bank and check its worth.

How to find out if your change is worth a mint

If you think that you might have a 'rare' £1 in there, you can use the Scarcity Index to check its value.

Lucky owners can also check how much coins are worth on auction website eBay.co.uk, or any selling platform. To find out how much coins have sold in the past, sellers should tick the 'sold' box on the left hand side on eBay, and rank your findings by 'value'.

Alternatively, you can choose to sell the coin to a specialist, like Changechecker.org or get it valued through the experts at The Royal Numismatic Society.