It looks like a black beetle until you see it close-up, when you notice its metallic bronzy sheen and bright crimson legs.
The Bronze Beetle, a type of leaf beetle, lives on ribwort plantain, as both adults and larvae feed on this plant. You can see that the beetle I saw was resting on some ribwort plantain leaves.
Bronze beetles aestivate during the height of the summer, which means they go into a state of dormancy to cope with the hot weather, so they can be seen from September round to June. In September, they wake up, start feeding again and lay eggs on the underside of the ribwort plantain leaves. Larvae hatch in the autumn, grow through four instars (stages) and pupate in the soil in the spring.