The first was a revival of Bridie's "Mr Bolfry" in 1956, in which Sim moved from the role of the puritanical clergyman to that of the Devil. The second was William Golding's "The Brass Butterfly", a 1958 comedy described by "The Times" as portraying the relations between an urbane Roman emperor (Sim) and a Greek inventor with wildly anachronistic scientific ideas (George Cole). In 1959, Sim sued the food company H J Heinz over a television advertisement for its baked beans; the advertisement had a voiceover sounding remarkably like him, and he insisted that he would not "prostitute his art" by advertising anything. He lost the case and attracted some ridicule for his action, but he was conscious of the importance of his highly recognisable voice to his professional success. Brooke comments on Sim's "crowning glory: that extraordinary voice. Only Gielgud rivalled his tonal control and sensitivity to the musicality of the English language." After doing little stage work in the 1950s, Sim resumed his theatre career in earnest in the 1960s. His range was wide, from Prospero in "The Tempest" (1962) and Shylock in "The Merchant of Venice" (1964), to the villainous Captain Hook in Barrie's "Peter Pan" (1963, 1964 and 1968) and the hapless Mr Posket in Pinero's farce "The Magistrate" (1969). The new plays in which Sim appeared were Michael Gilbert's "Windfall" (1963), William Trevor's "The Elephant's Foot" (1965) and Ronald Millar's "Number Ten" (1967); he directed all three productions. The first was dismissed by "The Times" as a tepid comedy about a progressive young headmaster thwarted by a reactionary member of his staff; the second, billed as a pre-London tour, started and finished in the provinces; the last was castigated by Philip Hope-Wallace in "The Guardian" as "maladroit playmaking" with a tedious plot about political machinations. Sim's performances provided some consolation: in the first, "The Times" said, his "treacherously sweet smiles, triple takes and unheralded spasms of apoplectic fury almost make the evening worth while". Much more successful among Sim's 1960s appearances were two productions at the Chichester Festival: Colman and Garrick's 1766 comedy "The Clandestine Marriage" (1966) and "The Magistrate".