Previous 50p designs have included beloved Beatrix Potter animals, Paddington bear and The Snowman. This is not the first time a children's book character has been honoured by the Royal Mint. It was adapted into a 27-minute animated film that premiered on the BBC on Christmas Day 2009 and was later nominated for an Academy Award. Writtenby Julia Donaldson and illustrated by Axel Scheffler, the book tells the story of a mouse taking a walk in a European forest and convincing other animals - including the terrifying Gruffalo - it is a fearsome creature. These new 50ps mark the 20th anniversary of the tale of The Gruffalo, which was published 20 years ago by Macmillan's Children Books and has sold more than 13.5 million copies worldwide. Some sellers will list coins at an inflated price, or bid on their own product, to make it seem more in demand than it is. A collectible coin is only worth what another collector is willing to pay for it.

However, treat eBay listings with caution.