I remember borrowing this book from my teens from a local library so some time in the mid-90's, although I can't be sure if it was new or old at the time.
The story was science fiction set in the UK based around a mist/fog which creates a barrier surrounding a town in England, trapping people inside and slowly shrinking with a view to obliterate the town in question. It may have been a dome that people couldn't escape or if it's just a fog they choose not to travel through, I'm unsure.
The story begins with I think a rather graphic rape scene - possibly between relatives - although I was in my teens so perhaps not actually that graphic. The reader is treated to an increasingly wider view of the local homes where all around normal people are acting out in strangely violent ways. I think the idea of the mist or fog is that it either made people violent or perhaps reduced inhibitions. There's also a vague memory that the fog/dome/whatever descends to encapture the worst of people (picking nasty towns in particular) and have them kill each other off, leaving no trace of the town in the end.
Sadly I cannot remember much more, but there was definitely 'townspeople' inside and you read about them surviving and coping with the sudden change. On the outside, the army and scientists are involved in dealing with the situation and one of the latter characters is an elderly scientist in a wheelchair. He eventually goes into the fog when they realise anyone they send in is disappearing/dying as he has 'nothing to lose' and goes in with a radio and on the end of a rope with a plan to pull him back if something bad happens. I have no recollection past this point in the book but I presume it was midway through as there was no resolution at this point - his rope goes slack and that's the end of him.
There's a brief conversation between scientists discussing that this phenomena had been seen before and simply removed towns/cities off the map completely.
I'm an avid sci-fi end-of-world reader, so it's possible one or more of these details has been mixed in from another story - please don't discount any possible ideas because not all are accurate! Finally, I can confirm that it's definitely not the recent Stephen King "Under the Dome", nor his novel "The Mist" or the James Herbert "The Fog".