Stag or lesser stag beetle?

I was starting to clear away part of a rotting tree stump at the back of the garden when I found seven or eight of these larvae. I'm not sure if they are the larvae of the stag beetle or lesser stag beetle. They were about 1.5-2 inches long and curled up when they were exposed.

I went off to check my identification guides and when I returned about 10 minutes later to take a closer look they had burrowed back under the remaining rotting wood. Rather than disturb them, I shall keep my eyes peeled and wait for the adults in order to determine which of the two beetles they are. From the information I've found so far I may have to wait at least a year or two if they are stag beetles.