In November 2008 a mix-up with the minting of the 20p coin meant that some of them don’t have a date. This is almost a perfect storm for collectors. A mistake on a coin’s design plus nobody knowing how many there are, has meant that this 20p coin can be worth a fortune. Recently one was sold on eBay for over £7,000
Less than 250,000 coins of the 136 million 20p pieces minted in 2008 – 2009 are undated. It happened because the Heads side from the previous design was used with the new Tails side design, meaning the year of issue did not feature at all.
These coins are still legal tender and most of them are probably still in circulation, so you should really check every 20p you find in your change.
The images below show the 2 correct designs from 2008 and the undated design. Check your 20p jar now. You might have a £7,000 coin sitting there doing nothing.