Just finished reading the Chryslaids with my 10 year-olds. Quite hard work but they liked it, found the evil future society deeply upsetting, as they should!
Now, Wyndham was def. a big deal in UK sci-fi, certainly for children, but it's only now that I noticed quite how much an influence this specific story may have had on Pat Mills re Nemesis the Warlock (it's all about religious zealots rooting out 'deviations') and on John Wagner re Strontium Dog (the mutants in this story all have minor but obvious physical deformities and are shunned by norms, and the odd few have mental powers...)
I kind of assume the book was so well-known in the late 70s that people just took these connections for granted but this specific book seems to have fallen out of fashion nowadays, it's all Triffids and Cuckoos.