He has performed in a large number of television productions, including guest roles in episodes of series such as The Black Adder where he played "Sean the Irish bastard" (1983) and Bergerac (1988), Sharpe (1994) and Doctor Who: "The Idiot's Lantern" (2006). He has also had major roles in more highbrow one-off productions and serials, including several instalments of the BBC's The Complete Dramatic Works of William Shakespeare (1982–83), most notably as Richard, Duke of Gloucester, later Richard III of England in Jane Howell's repertory treatment of the Henry VI plays and Richard III. He appeared as one of the unnamed "mysterious men" haunting the imagination of Michael Gambon's hospitalised Writer in Dennis Potter's acclaimed 1986 serial The Singing Detective, Jack Rosenthal British television play Day To Remember and has featured in several costume dramas, including Stephen Poliakoff's The Lost Prince (2002, as David Lloyd George), an adaptation of The Hound of the Baskervilles (2002, as Barrymore), a TV adaptation of The Other Boleyn Girl, (2003 as Thomas Cromwell), Anthony Trollope's adaptation He Knew He Was Right (2004, as Bozzel), and Russell T. Davies's Casanova (2005, as the prisoner in the cell next to Casanova's). In 2003, he played the part of Doughty, Admiral Pellew's and later Hornblower's steward in the Hornblower episode, Duty. In 2006, Cook appeared as Kenneth Williams' agent Peter Eade in the BBC biopic Kenneth Williams: Fantabulosa!, also in 2006 he played the role of Mr Magpie in the Doctor Who episode "The Idiot's Lantern".