[4] He was a Trotskyist and sought status as a conscientious objector in World War II, but was refused by his tribunal.
Symons highlighted the distinction between the classic puzzler mystery, associated with such writers as Agatha Christie and John Dickson Carr, and the more modern "crime novel," which puts emphasis on psychology and motivation.
His novels tend to focus on ordinary people drawn into a murderous chain of events; the intricate plots are often spiced with black humour.
In A Three-Pipe Problem (1975), the detective was "...a television actor, Sheridan Hayes, who wears the mask of Sherlock Holmes and assumes his character.
For his 1981 book The Great Detectives, he wrote a Sherlock Holmes pastiche instead of a biographical sketch.
He also made occasional forays into historical mystery, such as The Blackheath Poisonings (1978), which was filmed for television in 1992, and with Sweet Adelaide (1980).
[6] Symons died at his home at Walmer, in Kent, and was survived by his widow and son.