Dytiscus

Dytiscus is a genus of large (36 to 44 mm in length) predacious diving beetles of the family Dytiscidae represented by six species in Britain. They are dark brown, often with an olive-green reflection, and have a yellow marginal stripe. On the first pair of tarsi the male have one large, one smaller and a number of smaller still suction discs. Both
Found on http://www.probertencyclopaedia.com/browse/BD.HTM
No exact match found