Lonnen was best known for his role in the critically acclaimed spy series, “The Sandbaggers.”

Ray Lonnen, a British actor who played a spy in “The Sandbaggers,” a TV series that made the bureaucratic battles of espionage as gripping as 007-style cloak and dagger, died July 11 at his home in London. He was 74.

The cause was cancer, said his wife, actress and writer Tara Ward.

“The best spy series in television history,” critic Terrence Rafferty wrote in The New York Times in 2003. In a genre often pulsing with gadgetry and action, he singled out “The Sandbaggers” for its riveting look at complex office mind games and its stellar performances.

A tautly written 50-minute show, “The Sandbaggers” first aired on the British network ITV from 1978 to 1980, and reviewers noted that the program approached the caliber and nuance of a John le Carre miniseries, despite its low-budget production values.

“It was a great show about the process of doing these sorts of black ops and the process of bureaucratic infighting, which was almost comic in its elaborateness,” Rafferty said in an interview.

He added that its vicious and conniving anti-hero, Neil Burnside, a director of operations for British intelligence played by Roy Marsden, was unusually risky for audiences not accustomed to deeply flawed main characters such as the TV mafioso Tony Soprano. Lonnen portrayed Burnside’s loyal and best agent, Willie Caine.

“Ray Lonnen played a really important character in the show, because he was the only person for an ordinary viewer to identify with,” Rafferty said. “He was clearly a working-class type, the guy really doing the dirty work. Willie had a few more moral qualms than Burnside. Willie was a foil to a forbidding character who was very remote, very repressed, very buttoned up and hugely ruthless.”

A former paratrooper who does not like guns, Caine is sent on dangerous, sometimes dangerously compromised missions to rescue agents in the field, make contact with defectors and to seduce and kill when necessary.

Only 20 episodes were made before series creator Ian Mackintosh disappeared while flying in a small plane off the Alaskan coast in July 1979. No wreckage was ever found, and he was presumed dead.

Mackintosh was a former British naval officer who was coy about his involvement in covert operations. According to the book “The Life and Mysterious Death of Ian Mackintosh,” Lonnen said he repeatedly pressed Mackintosh to reveal whether he had ever been a spy by asking about plot twists on the show: “Did that happen Ian?” and “Would that have happened, Ian?”

“The replies were usually something along the lines of ‘It could have’ or ‘It might have,’ ” Mr. Lonnen said. “It was always difficult to get anything out of him.”