It is of the order Coleoptera.
Not 100% certain that it is hydrophilidae
No interactions present.
I believe that this is the larvae of the Great Diving Beetle (Dytiscus). There are several very similar species of GDB which are very hard to tell apart, so I assume the larvae are as well.
Chris Brooks - www.dragonfly-images.co.uk
My Flickr site - www.flickr.com/photos/ceb1298
Lat/Lng: 55.9575, -3.3246
OS grid ref: NT173746