This is the larva of the Stag beetle, Lucanus cervus. Where there is one there are usually more and they are best reburied in an undisturbed corner of the garden with the rotten wood they are feeding on.
Many trhanks AlteredEgo. I rather like the male SH beetle but I was sitting down up in the Lake District once (in shorts) & felt this seering pain in my leg. When I looked, there at right-angles, was this female SHB with her teeth firmly clamped into me.
Something about the female being more deadly that the male!!