(I am grateful to several people, particularly Robert Ilson and Moca Mace, for telling me about their acquaintance with Janet Whitcut.)
Janet Whitcut is important for our work as the author, along with Sidney Greenbaum (1929-1996), of The Longman Guide to English Usage (1988). Together, they revised Sir Ernest Gowers’s Complete Plain Words, of which one edition was published by His Majesty’s Stationary Office in 1986, while a third edition came out the year after that (Penguin).
Chloe White, one of the contributors to this blog, wrote a paper about the Longman Guide to English Usage and tried to find out who Janet Whitcut is (or was). But other than Sidney Greenbaum, Janet Whitcut has no entry in the Oxford Dictionary of Biography, nor in Wikipedia.

A Google search for her produced various book titles, including The Penguin Book of Exotic Words (1996) and Better Wordpower (Practical help on how to improve your use of the English language), Mastering English Usage (1994, written jointly with Robert Ilson) and Edgbaston High School, 1876-1976. Janet Whitcut also revised Partidge’s Usage and Abusage (1994). An article appeared as well, called “Sexism in dictionaries”, which is a paper she presented at the first EURALEX conference in 1983.

Dr Robert Ilson
Chloe was unable to find any trace of Janet Whitcut beyond 1999. Asking around didn’t help: David Cystal told me to contact Bas Aarts, who remembered meeting her thirty years ago, but that was it. Taking up the link with Robert Ilson took me to the website of Thornton’s Budgens, a “community supermarket”, which features Robert Ilson as their “poet laureate”. Is their picture of “Dr Robert Ilson” that of our man?
Robert Ilson’s name is familiar to me as the author of the article “Usage problems in British and American English”, published in a collection called The English Language Today (1985), edited by Sidney Greenbaum. And, yes, that produced another link: the collection also includes an article by Janet Whitcut: “English, my English?”.

Sidney Greenbaum
So even if this search has not told us much more of who Janet Whitcut is (or was), it did produce a small network of writers on English usage: Sidney Greenbaum & Janet Whitcut, Janet Whitcut & Robert Ilson, Sidney Greenbaum & Janet Whitcut & Robert Ilson. If Robert Ilson is the only one who is still alive, I hope he will read this and tell us more about his colleague and collaborator. But perhaps other people can help us, too.