Examining the photo' they seem however, to be Formica sanguinea, which according to Michael Chinery's "Collins Complete Guide to British Insects" ISBN : 978-0-00-729899-0 is "a rather rare ant [which] resembles the Wood Ant but its thorax is a brighter red and the legs are also much redder. The species is best known for its "slave raids" during which the workers invade the nests of related species and take away the pupae. The latter are installed in the sanguinea" nests, and when the adults emerge they work for their new mistresses. The nests are usually established in tree stumps in open woodland or on heathland." This is exactly what Ockham Common is like!
Black Garden Ants, Lasius niger, above and below, are tiny by comparison.
The other insect life was fascinating none the less. This fly looks like a Caddis fly.