Stag beetle larvae are hard to tell apart from some chafer larvae – easiest way is to put em down and wait. If it rolls into a C on it’s side, most likely a stag, if ittries to wriggle off on its front it’s most likely some sort of chafer.
So, now you know what it is what are you gong to do with it?
It was eaten by our resident blackbird a few minutes after I took the picture. It had been excavated from under the soil by a robin, which then appeared to consider the grub too much to handle. It was in the process of digging itself back underground when the blackbird stuffed it into its face.