Perhaps because of his early involvement in The Avengers, he often found work on shows that featured fantasy adventure, rather than the kitchen sink realism that had arisen in Britain at the start of his career.
Series with extraordinary lead characters in unusual circumstances, such as Department S, Jason King, Randall and Hopkirk (Deceased) and The Adventurer, dominated his output.
Following the demise of The Avengers, he worked on a number of programmes on which Dennis Spooner held some measure of creative control as creator or story editor, for ITC Entertainment.
His final script using the spy, Jason King's "A Page Before Dying", would mark the end of Williamson's longest association with a single fictional character.
[4] Williamson died during a second heart procedure in 1991, soon after his third film, a minor Roger Moore vehicle called Fire, Ice and Dynamite, opened in West Germany.