Her career spanned forty years and included roles in many British serials, including The Count of Monte Cristo (1956), The Vise (1959–1960), Danger Man (1965), The Saint (1967), as well as 1980's television series Just Good Friends and Minder. She starred in 1983's Screamtime, alongside Dora Bryan and Robin Bailey.He has appeared in numerous films and television programmes. He may be most famous for playing Cato (Fong), Inspector Clouseau's man-servant. The running gag was that Cato was ordered to attack Clouseau when he least expected it to keep him alert, usually resulting in Clouseau's flat being wrecked. Amid the chaos, the phone would ring and Cato would answer it with "Hello: Inspector Clouseau's residence," before dutifully handing the phone to his employer.
He was a stalwart of the ITC television film series when an oriental character was required. He co-starred in 12/13 episodes of The Sentimental Agent (1963).
Kwouk has appeared in three James Bond films. In Goldfinger (1964) he played a Chinese counterpart of Bond's; in the spoof Casino Royale (1967) he played a general and in You Only Live Twice (1967) Kwouk played the part of a Japanese operative of Blofeld.
In 1968 he appeared in The Shoes of the Fisherman opposite Laurence Olivier and Anthony Quinn. Kwouk also appeared as the honourable but misguided Major Yamauchi in the 1980s World War II television drama Tenko.
A reference to his appearances in several films with Peter Sellers is found in the opening scene of The Fiendish Plot of Dr. Fu Manchu where Sellers says to him "your face is familiar."
Kwouk featured in many UK television productions that called for a man of Oriental appearance. As a result, he became a familiar face in the United Kingdom and appeared as himself in The Harry Hill Show as well as several of Hill's live tours.
He enjoyed success as a classical stage actor, then played roles on British television. He was in the film Public Eye with Topol and Mia Farrow in 1970. Shakespearean roles on TV include Demetrius in A Midsummer Night's Dream (1968), Gratiano in The Merchant of Venice (1973) and Edmund in King Lear (1975). An early recurring television role was as civil servant Dowling in the final series of boardroom drama The Power Game in 1969.
In 1970 he played Henry Ireton in Cromwell. In 1971, he starred as Tsar Nicholas II of Russia in the film Nicholas and Alexandra, then in 1973 took the lead role of Mr Rochester in a BBC adaptation of Jane Eyre opposite Sorcha Cusack. He appeared as Gratiano opposite Laurence Olivier as Shylock in the National Theatre's film The Merchant of Venice (1974). He made two appearances in the anthology series Thriller in 1974 and in 1975 played Quiller, a spy who never used a gun, in the British TV series of the same name. He appeared as Dornford Yates' gentleman hero Jonathan Mansel in the 1977 BBC adaptation of She Fell Among Thieves. In 1979 he played Peter Guillam opposite Alec Guinness in the serial Tinker, Tailor, Soldier, Spy. He also played Mr Spooner in series Tracy Beaker Returns in 2010.
In 1986 Jayston played the role of the Valeyard in the long-running British science fiction television series Doctor Who. In the serial The Ultimate Foe, the Valeyard is revealed to be an evil version of the Doctor himself. He later reprised the part of the Valeyard in He Jests at Scars..., an audio play in the Big Finish Productions' Doctor Who Unbound series.
Jayston played Neville Badger in the 1989 television adaptation of David Nobbs's comedy of manners A Bit of a Do. He portrayed James Bond in a radio adaptation of You Only Live Twice in 1990. In 1991 he appeared as Colonel Mustard in the television series Cluedo and a year later made a guest appearance in the Press Gang episode "UnXpected". Other TV appearances include in EastEnders, Coronation Street, Only Fools and Horses, The Darling Buds of May, Tales of the Unexpected, The Bill and the character of Donald De Souza in Emmerdale. He also was on Holby City and Tracy Beaker Returns as Mr Spooner, who was the old man was the owner of the mobility scooter that Liam O'Donovan stole.