Great Diving Beetle one of three caught when children from Meadowgate School were dipping on an ice covered Surrey pond.
No interactions present.
There are a few species of Dytiscus which are not separable without looking at some rather fine details on the underside. You certainly can't use this picture to make it marginalis, and unless you did the technical stuff at the pond it would be safer to call it Dytiscus sp.
recording wildlife with The Recorder's Year on www.hbrg.org.uk/TRY.html.
Lat/Lng: 51.149504655304, -0.44667363166809
OS grid ref: TQ087400