Set in a disintegrating Britain of the near future, brought to its knees by global warming, rising sea levels, disease, unemployment and pollution. The rich live in enclaves surrounded by electrified fences and security cameras, mobs of urbanites roam the country looting and pillaging and the government maintains a shaky control over the county by controlling the dissemination of information and discouraging travel. It's a very believable future, and all the more disturbing for that.
The main characters are ex-rock star Richard Sommers, living in a mansion in Dorset in the enclave centred on the village he grew up in, and his sister Hannah-Rose, the proprietor of a travelling dance troup. When Hannah-Rose finds a computer disk containing an unpublished novel written by their author father, it precipitates a crisis that forces them out of their comfort zones, and changes both their lives. The novel (although it doesn't seem much like a novel to me), is the story of man's evolution, based on the aquatic ape theory.
When I finished, I had a look on my bookcase and found that I still have my copy of "The Aquatic Ape" by Elaine Morgan, which I bought in a library sale in 1989 and which is one of Thomas Somers' sources for his novel.