Prematurely balding and greying, Vernon settled into playing archetypal middle-aged lords and military types while still in his 30s.

At the end of his service, his commanding officer reported "Vernon is an excellent dinghy helmsman and amateur actor: in his spare time he performs his duties satisfactorily.

An early leading role was as wartime agent-turned-criminologist Edwin Oldenshaw in the TV series The Man in Room 17 (1965–66) and its sequel The Fellows (1967).

[6] He played an unnamed 'city gent' reluctantly sharing a train compartment with the Beatles in A Hard Day's Night, planet designer Slartibartfast in the BBC radio and TV series The Hitchhiker's Guide to the Galaxy, the occasional character Sir Desmond Glazebrook in the TV series Yes Minister and Yes, Prime Minister, and Mr Becket in Sammy's Super T-Shirt.

[7] He also appeared in the 1965 Morecambe and Wise film The Intelligence Men as patron of the arts Sir Edward Seabrook, Lord Bartelsham in Ripping Yarns, and Squire Dale in the BBC Radio 4 adaptation of The Small House at Allington.

[10] He played the urbane head of the Secret Intelligence Service Sir James Greenley in ITV political drama The Sandbaggers from 1978 to 1980.