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It actually cost me £23, which included £3 P+P. Its presented in a really nice slip case. What the Mint normally does is to issue more fancier versions.
later on. This one is brilliant, uncirculated. Not sure what the difference is between brilliant, uncirculated and "proof" though.
I have done some research this morning on the 'net, and it appears that silver is 42p a gram, so this coin, weighing in at 15.71g, is only worth £6.59 in the silver alone. So, not quite such a bargain at £20, although that is not why I bought it.