An English-born writer of thriller novels, he is best known for his 1971 work, The Freedom Trap, which was adapted into a film starring Paul Newman. His other novels include High Citadel (1965) and The Tightrope Men (1973).
He dropped out of school and worked in a factory and in a printer's office. He published his debut novel, The Golden Keel, in 1963.
In 1947, he moved to South Africa, where he worked as a freelance writer for magazines and newspapers.
He was the son of Hannah and John Bagley. In 1960, he married Joan Margaret Brown.
His novel, The Enemy, was adapted into a film starring Roger Moore.