4 large black birds in trees near a small lake
No interactions present.
Like you thought, the white patch on the side (thigh area) is something that adult Cormorants get in the breeding season. Some also get a lot of white on the head when they are in breeding plumage (this is especially common for those of the continental race, sinensis, but British race birds can also develop white heads).
Lat/Lng: 52.7, 0.9
OS grid ref: TF9918