There appears to be a healthy Lesser Stag beetle population in the neighbourhood. Only in my street, I have come across at least six individuals (unfortunately, two of them had been squished on the pavement) in four years. So far, however, I had only seen females, and I was pleased to find a fierce-looking male this morning. This species is often mistaken with Stag Beetles. But Lesser stag beetles are smaller and uniformly black-grey with fine puntuated bodies. They have strong legs with teeth which they use for digging, especially the females, and, when disturbed, they crouch and retract their legs and antennae under their bodies. Although they are not as easy to sex as the Stag Beetle, males and female Lesser Stat Beetles can be told apart based on several features. First, males have larger mandibles, with a rounded knob on them. Females have two characteristic small bumps on their forehead, between their eyes. The third one is that male heads are wider, almost as wide as their thorax, and therefore their mandibles are also set wider apart. Based on the photos and info I've seen, it appears to be a lot of variation on body size (from 20 to 32 mm) and in knob size in males.
For lots of information about the life cycle of the Lesser Stag Beetle and relatives visit Maria Fremlin's website.