The 20p coin that could make you a mint!

Have you ever noticed something particularly unusual about one of your coins? Perhaps a missing date, denomination or an error in the design?

Well, that’s what happened to one collector who noticed something unique about their 20p coin…

A ‘spectacular error’

The 20p in question was minted in 1990 for a British overseas territory, and was sold as part of a set. However, instead of having the usual cupro-nickel finish, it was struck on a copper-plated blank intended for a different country.

The 20p error coin
A ‘spectacular error’ occurred on this 20p coin
Credit: SWNS

Collector, Alun Barker saw this unusual coin listed on eBay in December 2017 and bought it for just £50. But he was pleasantly surprised when, just a month later in January 2018, the coin was confirmed as a genuine error by The Royal Mint, who issued a certificate of accreditation. They also confirmed it was the only known 20p in existence with with error, making it one of a kind!

Exceeding expectations at auction

Alun decided to have the coin valued by specialists, Tennants Auctioneers, who initially estimated it could fetch as much as £1,200 at auction. However, when he decided to part with the coin in August 2023, Alun was astonished to find out it had sold for a whopping £1,400!

Tennants Auction Centre
Tennants Auction Centre, North Yorkshire

Not the first rare 20p error…

The ‘Bronze 20p’

In 2017, collector David Crosier found a 20p coin with an unusual finish, which he assumed to be bronze plated. He sent the coin to The Royal Mint to check, and after x-ray fluorescence spectrometry, they confirmed it was a genuine minting error.

The 'bronze 20p' with a 20p and 1p from the same years
The ‘bronze 20p’ with a normal 20p and 1p from the same year

Somehow, a 1p blank had made its way into the presses and a 20p was mistakenly struck onto it.

Find out more about this extremely rare error coin >>

The undated 20p

Considered by many as the ‘Holy Grail of change collecting’, the undated 20p is undoubtedly at the top of most serious collectors’ wish lists. In 2008, an unknown number of 20p coins were released into circulation without a date on either the obverse or reverse. This followed a die mix up after the new Royal Shield design was introduced.

Undated 20p reverse and obverse
Undated 20p reverse and obverse

The Royal Mint confirmed this was the first time in over 300 years that a coin had entered circulation without a date, making it extremely sought-after by collectors. They also confirmed that, whilst exact quantities are unknown, no more than 250,000 of these undated coins made it into circulation.

These coins have been listed on the secondary market with a value as high as £10m, however you should always check the sold listings on secondary market sites to see how much collectors are actually willing to pay for a coin.

Our latest eBay Tracker shows that the undated 20p is currently selling for around £52.

Find out more about the undated 20p >>

Have you ever found an error coin in your change? Let us know in the comments!


  1. Jordan on September 29, 2023 at 12:32 pm

    I have a two pound coin with the L not printed on the shoulders of giants £2 coin I also have a 20p that’s in real bad shape but under a microscope it looks made that way , can provide photos to anyone for their opinions

  2. Kelly on September 15, 2023 at 10:21 pm

    I have a Peter rabbit coin with a copper line through it

  3. Terri D on September 14, 2023 at 12:48 pm

    In 2008 I had an undated 20p. Being a numismatist, I wanted to keep it but idiot ex sold it. Every time I get given change, I always check it, hopefully

  4. Trevor Foster on September 14, 2023 at 12:28 pm

    I have a Gibralta 20 pence piece. I think it’s a 2013 issue with 4 keys on the obverse side that has been struck off centre. Who do I need to contact to get it verified.

    • Kate on September 19, 2023 at 11:21 am

      Hi Trevor, sounds like an interesting find! I’d probably suggest contacting the Gibraltar National Mint to have it verified as a genuine error.
      I hope that helps, Kate

  5. J J C HARDING on September 14, 2023 at 12:07 pm


    • Kate on September 19, 2023 at 11:19 am

      Hi, sounds like you’ve found a rare error coin! We’d suggest sending it to The Royal Mint to have it verified as a genuine error, after which you can use our 6 point guide to valuing your coins if you wish to sell it.
      I hope that helps, Kate

  6. Daniel Wright on September 14, 2023 at 6:29 am

    I used to have a mule 20p – sold mine on EBay in 2013 for £45; but after EBay and PayPal fees at the time, I got a little over £36.

    Part of me wishes I kept it now, but I wasn’t as much into coin collecting back then as I am now.

  7. Costin Constantinescu on September 14, 2023 at 5:03 am

    I found mine in 2014,after 6 years of checking,being a taxi driver.I could sell it for 2 000 pounds.

  8. Stephen on September 13, 2023 at 8:27 pm

    I’ve got a new pound coin with part missing on sides

  9. Steve powell on September 13, 2023 at 6:19 pm

    I have 5 of the undated 20p – good one to collect

  10. Philip Pavlovic on September 13, 2023 at 4:07 pm

    Yes I found the mule 20p in my change one day.
    Don’t know whether keeping hold of it will increase the value though!

  11. Julian Berkeley on September 13, 2023 at 3:24 pm

    I once owned a shilling with just an obverse! It appears that a blank had entered the process on top of a coin that had been struck, so the obverse was correctly struck in the blank, but the reverse had a concave version of the Queen’s head struck into it. I sold it years ago, before the advent of digital photography, so have no record of it, sorry!

    • Tee Em on September 13, 2023 at 4:41 pm

      I have a 1p coin that’s only printed on one side from the 1970s.

  12. Ashleigh on September 13, 2023 at 3:02 pm

    I have a 5p the size of a 10p and I also have this 20p coin