Brigid was a novelist, critic, and campaigner for social reforms, including the rights of authors and animal rights. Her 1965 Sunday Times article is credited by psychologist Richard D. Ryder (another Sentientist) with having triggered the formation of the animal rights movement in England. Brigid was one of the signers of the Humanist Manifesto and was president of the National Anti-Vivisection Society.
Brigid wrote that she and her father were "natural, logical and happy atheists". She said: "Reason can always disarm the irrational. If reason finds itself to be irrational, it can disarm it; and if one finds reason and discovers that eating animals is immoral, unnecessary, and done largely for superstitious reasons, then one is delivered from the compulsion to do it."