Plot revolves around young women who find that when they mature they will only give birth to girls.
Possibly Implosion (1967) by Dennis Feltham Jones.
The release year matches, D. F. Jones was British, and sterility is used as a weapon. However, the remaining fertile women find themselves only to bear boys, not girls. (still warrants the end of humanity, though)
Implosion is a science fiction novel by British writer D. F. Jones, published in 1967, set in a United Kingdom just attacked by an unnamed minor Eastern Bloc country. The weapon used, 'Prolix', is a chemical sterilant, that, once ingested, renders most women sterile.
The protagonists are the Minister for Health, Dr. John Bart, M.D., and his wife Julia; he soon finds his Ministry is the most important government entity in the new, post-attack Britain, while his wife is one of the country's few remaining fertile women. In the end, as the Minister for Health, Dr. Bart finds himself creating a new society where fertile women are herded to concentration camps, to spend the rest of their lives reproducing.
Meanwhile, the rest of the world are shooting Prolix at each other, gradually reducing their populations to Britain's circumstance. At story's end, mankind learns that the genetic quirk that kept some women fertile allows them to only bear boys, thus dooming humanity to extinction.
Found by searching this site for
[story-identification] infertile, Implosion was suggested (but denied) as an answer to Book about infertility.