[1] He also made many television appearances, which included portraying Peter Guillam in the miniseries Tinker Tailor Soldier Spy (1979), playing the Valeyard in all fourteen episodes of the Doctor Who serial The Trial of a Time Lord (1986), and appearing in the Only Fools and Horses episode "Time on Our Hands" (1996) as Raquel's father, James.

[4] Jayston began his stage career in 1962, performed at the Bristol Old Vic, and joined the Royal Shakespeare Company at Stratford-upon-Avon in 1965.

[1][4] He starred as Captain von Trapp in the 1981 stage revival of The Sound of Music at the Apollo Victoria in London's West End, alongside Petula Clark as Maria.

In 1984, Jayston starred as Mirabell in a production of William Congreve's The Way of the World at the Haymarket Theatre opposite Maggie Smith and Joan Plowright.

An early recurring television role of his was as civil servant Dowling in the final series of boardroom drama The Power Game in 1969.

Other TV appearances include in EastEnders, Coronation Street, Only Fools and Horses,[1] The Darling Buds of May, Tales of the Unexpected, The Bill and the character of Donald De Souza in Emmerdale.

He appeared in Foyle's War, Holby City, Sherlock Holmes, Tracy Beaker Returns, and Midsomer Murders.

Jayston recorded most of John le Carré's novels in audiobook format,[8] providing a link with his role as Peter Guillam in the 1979 TV series Tinker Tailor Soldier Spy.