I'm thinking Pterygoplichthys pardalis, which is apparently the most common "common plecostomus" in the trade currently, and which are really variable (with age, I think) and often have these pale bands. But there are a bunch of similar species in the big plecs.
@Chlidonias Thanks - some of the pictures in that link certainly do look very similar to the Colchester fish. I'd be comfortable saying that it is Pterygoplichthys pardalis.
