Hazel Adair, who along with Peter Ling created the soap operas Compact and Crossroads, but also earlier in her career co-wrote (with Ronald Marriott) a childrens' sf series, Stranger from Space, the adventures of a Martian boy who has crashed on Earth and is befriended by a human boy, which had two series in 1951-2 and 1952-3 (shown as an insert into the magazine programme Whirligig).
Sheilah Ward, who was married to Peter Ling (himself the author of a Troughton-era Doctor Who story), wrote a 1958 children's sf series for ITV, Time Is The Enemy (as well as a couple of episodes of The Avengers).
Evelyn Frazer, who wrote an sfnal play, "The Critical Point", broadcast in 1957 and again in 1960, mixing cryogenics with police procedure. She also wrote Virus X, a 1962 play featuring a supervirus, and later in 1962 wrote a four-part series called The Monsters with Vincent Tilsley.
Marielaine Double has precisely one IMDB credit, as co-author of the 1965 Wednesday play Campaign for One, a "psychological space drama" according to Keith Topping.
Marghanita Laski, better known as a journalist and non-genre writer, but also author of a post-apocalypse play, The Offshore Island, which was broadcast in 1959.
Elaine Morgan, now better known for her advocacy of the aquatic ape hypothesis, wrote (among many other TV credits) Thunderbolt, an episode of R3, a drama series set in a secret British government research unit - the Bugs or Torchwood of its day.
Kate Wilhelm is not British, but her short story Andover and the Android was adapted by Bruce Stewart as a 1965 episode of Out of the Unknown. (The story was published in 1963 in a collection called The Mile-Long Spaceship; when it was published in the UK in 1966, the title was changed to Andover and the Android, presumably to make the most of the TV tie-in.)
In 1966, the Doctor Who time slot was filled over the summer by an sf children's detective series called Quick, Before They Catch Us, whose fourth and final story, "The Tungsten Ring", was written by Margot Bennett and directed by Paddy Russell. Bennett is much better known as a crime writer, though one of her other books has the intriguing title of The Intelligent Woman’s Guide to Atomic Radiation.
Finally, Keith Topping lists a couple more female writers of sfnal TV plays in the Thirty Minute Theatre strand: Dawn Pavitt, who co-wrote "The Isle is Full of Noises" with Terry Wale in 1965, and Charlotte Plimmer, who co-wrote "Standing by for Santa Claus" with Denis Plimmer in 1968. Both of them have a few other IMDB credits which may or may not be sfnal.
I am sure there are more. Hazel Adair in particular looks like she merits some further research.