Captivep:-
I thought it had pretty well established (and, indeed, confirmed by HMG) that the body used was that of Glyndwr Michael
In all likelihood we'll probably never know for sure. Geriaviator is correct, there was indeed speculation that 'Major Martin' was a victim of the explosion on HMS Dasher, offering a more convincing corpse than that of Michael. The transhipment onto HMS Seraph was via Scotland anyway, but the ID docs would have needed to reflect the 'new' man. No doubt it could be done, and given the national security implications involved, if it was done then the only evidence of it left would be in their respective graves. Hopefully they will remain there, undisturbed. Some stories are better left with a perpetual question mark hanging over them....