This is a female Stag Beetle, which is waiting for a mate. Male Stag Beetles have big horns and that is how I can tell the difference.
I took this photo in my garden in June when stag beetles were flying around and mating. this was unusually late as they usually are around in May but it was delayed this year because of the cold weather.
Stag Beetles are quite rare but there are a lot where I live in South-East London. We see lots every year.