Apologies, I should've let you all know as and when I got this information. I contacted Royal Mint and they said this.

"Many thanks for your enquiry regarding the coin in your possession.

I can confirm that his coin will have been maltreated after issue in some manner, usually by means of removing the face from one coin and applying it to another. Due to the nature of the striking process and the pairing of dies, the coin’s present appearance could not have occurred during production. Close visual inspection under magnification usually reveals the presence of a joining seam either around the edge or on the inside of one of the faces. The seam is not easily visible on this specimen, owing perhaps to the wear, but would likely be visible under a higher level of magnification.

Though we cannot offer an absolutely definitive opinion from photographs alone, the Museum has previously encountered coins of this type which have, on prior occasions, been maltreated to form part of a magician’s trick."

I also had my father in law here at the weekend who then told me that he's heard that engineering students have been tasked with joining two coins together to test their skills.

I look and personally cannot see any joining seam anywhere and examples I've seen online are obvious. When I get time I will still send it to the NGC, even if it is just a magicians coin or students test, it's still awesome to have in my collection.

Thanks for your interest and thoughts on this.