He appeared in many films after a significant role as Dim in Stanley Kubrick's A Clockwork Orange.

Clarke's first television appearance was in the long-running Granada soap opera Coronation Street, initially as Kenny Pickup in 1966 and then as Gary Bailey in 1968.

His first major film appearance was in Stanley Kubrick's A Clockwork Orange (1971) where he played a "droog" named Dim opposite Malcolm McDowell.

Clarke appeared in a wide range of roles in television and film productions including The Breaking of Bumbo (1970), Home (1970) opposite Sir Ralph Richardson and Sir John Gielgud, Charlton Heston's Antony and Cleopatra (1972), Jennie: Lady Randolph Churchill (1972), "The Frighteners", (ep.4.The Minder), (1974), Tinker Tailor Soldier Spy (1979), S.O.S.

Titanic (1979), ‘’Hammer House of Horror,(se1ep2) (1980), Hawk the Slayer (1980), Masada (1981), Tales of the Unexpected: Never speak ill of the dead (1981), Enigma (1982), Lassiter (1984), Top Secret!

The same year he played the role of Martin Fisher, the chairman of a football club, in The Manageress and the role of Managing Director of an engineering firm, Vic Wilcox, in the TV adaptation of the David Lodge novel Nice Work.

[3] Between 2000 and 2003, Clarke played Brian Addis, a father who moved his family from the bustle of London to a Devon farm, in the BBC TV series Down to Earth.

Around the same time, Clarke appeared as Commander Peters in the ITV production of Agatha Christie's Marple Why Didn't They Ask Evans?

The character's final scene in the series, in episode four in which Poldark lies on his deathbed before dying, was also Clarke's final scene as an actor: he was very ill at the time of filming and died a few weeks later; the first episode of the television series was then dedicated to his memory.