It was, he thought, the fruit of many years spent in repertory in the 1950s and 1960s. In this training ground he learned to bring to life a huge gallery of characters, and he went on to enjoy many successes on television, for example as the crusty, ageing head of the family in The Cazelets and as Colonel Leyton in the hit series The Jewel in the Crown.

Frederick William Treves was born at Margate, Kent, on March 29 1925, the son of a GP who had commanded the South-East Mounted Field Ambulance Brigade in the Middle East during the Great War. Freddie’s great-uncle was Sir Frederick Treves, 1st Bt, Serjeant Surgeon to Edward VII, whose appendix he removed two days before the Coronation planned for June 26 1901 ; Sir Frederick was also noted for bringing Joseph Merrick (“The Elephant Man”) to live at the London Hospital in the 1880s.

After the Nautical College, Pangbourne, Freddie joined the Merchant Navy at the age of 17. While serving in a convoy seeking to relieve Malta, he was one of the few survivors when his freighter, Waimarama, which was carrying high explosives and aviation fuel, was sunk on August 13 1942. Treves saved the life of Radio Officer John Jackson, and was awarded a BEM.

After the war he went to Rada, where he won the Emile Littler prize. His first West End role was as a Persian soldier in Terence Rattigan’s The Adventure Story in 1949. He then played extensively in rep around the country and had various West End parts. In 1976 he appeared in Tom Stoppard’s long-running Dirty Linen at The Arts.

After joining the National Theatre in 1978, Treves was in Shaw’s Philanderer and played Sir Andrew Charleson in David Hare’s Plenty. Other National roles included Leonato in Much Ado About Nothing (Olivier) and Menenius Agrippa to Ian McKellen’s Coriolanus (Olivier, 1984).

But it was on television that Treves really made his mark, appearing in countless series that became the staple diet of British audiences, among them Rumpole of the Bailey, Kavanagh QC, Heartbeat, Casualty, Bergerac, The Bill, Lovejoy, Yes, Prime Minister and Jeeves and Wooster . One year, he “died” on screen no fewer than seven times.

His films included Defence of the Realm; Nighthawks; and The Elephant Man, in which his great-uncle was played by Anthony Hopkins and Treves appeared in the character of an alderman.

He married, in 1956, Jean Stott, who survives him with two sons and a daughter. One of his sons is the actor Simon Treves.

Frederick Treves, born March 29 1925, died January 30 2012