Jonathan Cecil: Actor who specialised in upper-class twits and found his perfect role in Bertie Wooster

Playing the perennial upper-class twit provided Jonathan Cecil with a career in acting that lasted almost 50 years. The role of "silly ass" Bertie Wooster in the 1981 BBC television film Thank You, PG Wodehouse, marking the centenary of the humorist's birth, and reading more than 40 audio recordings of the writer's books, fitted the actor like a glove.

But Cecil was most commonly seen on television as a foil to others. This was epitomised when he joined the sitcom Romany Jones for its third and fourth series (1974-5) as Jeremy Crichton-Jones, who lived with his wife, Susan (Gay Soper), next to Wally and Lily Briggs (Arthur Mullard and Queenie Watts) – on a caravan park. The setting was unlikely, but it brought together Cecil and the growling cockney Mullard's chalk-and-cheese characters to give the programme – created by Ronald Wolfe and Ronald Chesney – a new comedy angle when the death of one of its original stars, James Beck, made a revamp necessary.

Such a stock-in-trade meant that Cecil joined a small band of actors who were most frequently considered for snooty buffoons. Earlier this month, the performer-turned-screenwriter Julian Fellowes said of his own acting career: "I was the silly ass who fell down the stairs or the fascist government minister. I seemed to spend a lot of my time competing for roles with a particular group of actors. There was Jeremy Childs, Jonathan Cecil, Jeremy Sinden and Simon Callow – and me."

Cecil was made for such parts, having been born into the aristocracy shortly before the outbreak of the Second World War. His father was the author and academic Lord David Cecil – son of the 4th Marquess of Salisbury – and his grandfather was the drama critic Sir Desmond MacCarthy.

As a child, Cecil gained a love of Shakespeare and pantomime in Oxford, where the family lived when his father was Goldsmith professor of English at the city's university. He was also influenced by radio comedy.

After attending Eton College, Cecil gained a BA in French from New College, Oxford, where he acted with the Oxford University Dramtic Society alongside Dudley Moore and Alan Bennett. He then trained at LAMDA and, after being seen in his final performance there by the BBC television director Naomi Capon, was cast in a leading role as a student, alongside Vanessa Redgrave, in the play Maggie ("First Night", 1964).

Other television parts quickly followed, including Cummings in The Diary of a Nobody (1964), Ken Russell and John McGrath's adaptation of George and Weedon Grossmith's comic novel. Russell directed it as a silent film, with a voice-over and the cast deliberately over-acting.

Cecil performed with repertory theatre companies in Northampton, Dundee, Hornchurch, Salisbury and Lincoln, and made his West End début in A Heritage and its History (Phoenix Theatre, 1965), Julian Mitchell's adaptation of the Ivy Compton-Burnett novel. Two years later, he acted Basil Utterwood, alongside Robert Morley, in Peter Ustinov's play Halfway up the Tree (Queen's Theatre, 1967), directed by John Gielgud, who said after auditioning Cecil: "Splendid! Splendid! You know, I've had to watch all these terribly nice young men coming on the stage and trying so desperately hard to look gangly and absurd, and they just can't do it. And then you can come on and just stand there and do nothing, and... Oh, I'm terribly sorry. I didn't mean..."

Cecil appeared in other West End productions such as The Ruling Class (Piccadilly Theatre, 1969), Lulu (Apollo Theatre, 1970), Uncle Vanya (Vaudeville Theatre, 1987-8) and As You Like It (Globe Theatre, 1997-8), but his favourite stage role was Sir Andrew Auguecheek – and the line "I was adored once" – in Twelfth Night, which he took four times during his career.

He also performed a one-man show, The Incomparable Max, at various venues (1994-96). It featured the work of the English essayist and parodist Max Beerbohm, who was the subject of one of his father's biographies.

Television provided a steady stream of work for Cecil, including guest roles in comedies such as Doctor in the House (1969), Dad's Army (1973, as a military dog-training school administrator), It Ain't Half Hot Mum (1977), Murder Most Horrid (1994) and One Foot in the Grave (2000). He was a regular as Mr Herbert in Oh Happy Band! (1980), a coolly received sitcom written by David Croft and Jeremy Lloyd about a brass band conductor (Harry Worth) leading a campaign against plans to build an airport.

Cecil particularly enjoyed playing Hastings, Poirot's assistant, alongside Peter Ustinov, in the television films Thirteen at Dinner (1985), Dead Man's Folly (1986) and Murder in Three Acts (1986). In the second series of the BBC radio version of the clerical sitcom All Gas and Gaiters, broadcast in 1972, he stood in for Derek Nimmo – who had other commitments – as the Reverend Mervyn Noote, the bishop's chaplain.

Among the actor's more interesting roles in the cinema was Ricotin – whom he described as "a white-faced, crypto-homosexual film clown" – in Federico Fellini's 1973 picture And the Ship Sails On, about a group of illustrious friends accompanying the ashes of a great opera singer on a transatlantic cruise to her final resting place. He also appeared in the Hammer horror film Lust for a Vampire (1971), Barry Lyndon (1975, directed by Stanley Kubrick), Joseph Andrews (1977, directed by Tony Richardson, in which he was, typically, credited as "Fop One"), History of the World: Part I (1981, directed by Mel Brooks), Little Dorrit (1988) and As You Like It (1992).

Enjoying some success as a writer, Cecil contributed book reviews and other articles to The Spectator and various newspapers. His first marriage, to the actress Vivien Heilbron, ended in divorce. He met his second wife, the actress and singer Anna Sharkey, when they were both in the Noel Coward musical revue Cowardy Custard (Mermaid Theatre, 1972). Together, they later conceived a stage show, Plum Sauce, in which he read excerpts from PG Wodehouse's works and she performed songs.

Jonathan Hugh Cecil, actor and writer: born London 22 February 1939; married 1963 Vivien Heilbron (marriage dissolved), 1976 Anna Sharkey; died London 22 September 2011.