I found this grub when tending to my leaf mould pile. The pile was made up with the 2014 autumn leaves and has been undisturbed since then. The grub is about 5cm long. I am unsure whether it is the larva of a stag beetle or a cockchafer since I get both species emerging in the garden in early summer.
I returned the grub carefully to a part of the pile that will not be disturbed for some time.