Willie Caine, played by Ray Lonnen, and Neil Burnside, played by Roy Marsden, on the TV spy show “The Sandbaggers.” Mr. Lonnen died July 11 at 74. (ITV/Rex/REX USA)

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. He singled out “The Sandbaggers,” part of a genre often pulsing with gadgetry and action, 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 1978-1980, and reviewers noted that the program approached the caliber and nuance of a John le Carré 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 who would have been unaccustomed to deeply flawed main characters, such as the TV mafioso Tony Soprano. Mr. 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.”

Caine, a former paratrooper who does not like guns, 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 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,” Mr. 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.”

“The Sandbaggers” did not attract a large audience. A fan Web site calls it “the best damned television show you never saw.” But it grew a devoted following — particularly among prominent critics such as Marvin Kitman at Newsday — as the series was rebroadcast on U.S. public television and as Marsden went on to greater fame on TV playing P.D. James’s poetry-writing Scotland Yard sleuth Adam Dalgliesh.

Raymond Stanley Lonnen was born May 18, 1940, in the southern English coastal town of Bournemouth. After attending drama school in his home town, the ruggedly handsome and rakishly appealing Lonnen became a familiar presence on British television and stage.

He was a police detective in the long-running crime drama series “Z-Cars” in the 1970s and had a starring role in the gritty miniseries “Harry’s Game” (1982), based on the best-selling Gerald Seymour novel about a British soldier who goes undercover to capture an Irish Republican Army assassin.

Mr. Lonnen remained an active TV performer through recent years, often on police shows such as “Yellowthread Street” and “The Bill” but also on the animated series “Budgie the Little Helicopter.” He also was a prolific voice-over artist for audiobooks­ and commercials.

His first marriage, to actress Lynn Dalby, ended in divorce. In addition to his wife of 20 years, survivors include three children from previous relationships and two sisters.

“Ray loved puns and limericks and had a wonderful sense of humor,” his wife, Tara, wrote in an e-mail. “When talking of his start in the precarious acting business, he used to say when he left school he worked in a mattress factory for a while — so he would have something to fall back on.”