An interesting article from our friend Jeff Starck over at Coin World on Britannia errors
We'll look into this and let you know more when we find out!
*update* apparently these do exist - Jeff was in contact with Llantrisant and they confirmed the existence of the mules.
The official statement from the RM is as follows:
Some of our recent bullion customers may have noticed a slight change in the design of the edge decoration of our UK 2014 £2 Britannia bullion coin, and the UK 2014 £2 Lunar bullion coin.The variation of the design has been struck on approximately 17,000 Britannia and 38,000 Lunar coins for a limited time only. The quality and value of the coins remains the same.