Chapman Pincher died on Aug. 5 in England. He was 100 years old. (PA Wire/Press Association Images)

Chapman Pincher, a reporter and author who plagued prime ministers and tracked down traitors while becoming a legend in British journalism, died Aug. 5 in England. He was 100 years old.

He had a small stroke several weeks ago, his son, Michael Chapman Pincher, told Britain’s Guardian newspaper.

As an investigative reporter for the London Daily Express, Mr. Pincher flourished throughout the Cold War decades, displaying a flair for getting highly placed sources to entrust to him with information that many in Britain’s political and security establishments wished to keep secret.

Working as a one-man investigative unit, Mr. Pincher sought to expose the activities of people he suspected of acting surreptitiously on behalf of the Soviets. In an interview with Mr. Pincher last year in the British newspaper the Independent, Charlotte Philby noted that one of the traitors or double agents he exposed was her grandfather, Kim Philby, who defected to the Soviet Union in 1963.

Mr. Pincher was dubbed “the great spy catcher of Fleet Street,” after the street that was the headquarters of British newspapering.

Targets of Mr. Pincher’s suspicions included other members of the “Cambridge Five,” a group of British intelligence moles — including Philby — educated at Cambridge University; the German atomic spy Klaus Fuchs, who was convicted of leaking information about allied nuclear research to the Soviets; and even one of the chiefs of the British internal security agency MI5, analogous to the FBI.

The suspicions about the MI5 chief came in a 1981 book “Their Trade Is Treachery,” which was published after Mr. Pincher had left a 40-year career in newspapers. Some of his allegations were vigorously denied.

Mr. Pincher was unruffled by critics who said he was reporting leaks to serve the purposes of his source, saying, “If someone wants to come and tell me some news that nobody else knows and I make a lovely scoop of it, come on, use me.”

In addition to his revelations of spying, Mr. Pincher also broke journalistic ground with reporting on the link between smoking and lung cancer and was credited with a scoop on the marriage of Britain’s Princess Anne.

Endowed with a memory that enabled him to recall what he was told without recourse to note-taking, Mr. Pincher often interviewed his sources at his favorite London tavern. One chapter in his autobiography, “Dangerous to Know,” published this year to mark his 100th birthday, was called “Momentous Lunches.”

Mr. Pincher was equally adept at getting information by joining well-placed weekenders in countryside fishing or shooting outings.

“I always tried to meet all the top people because that’s where the stories lay,” he once said. “When you have access to people, you have access to facts, usually secret facts.”

Such practices allowed him to set out in disturbing detail the extent to which Britain’s security services had been penetrated by the Soviets. Noting the unusually large size of the Soviet embassy in London, Mr. Pincher asserted that many of the presumed diplomats, gardeners and drivers were actually engaged in espionage. Ultimately more than 100 were expelled.

In another revelation, Mr. Pincher told Britons how the government was intercepting their private cables and telegrams. According to news accounts, he also detailed overpayments for the Bloodhound missile, a mainstay of Britain’s air defense.

While head of the defense staff, Lord Louis Mountbatten was said to have dictated a story to him, as the two drove together. The story appeared under Mr. Pincher’s name.

One of the most frequently repeated endorsements of his journalistic accomplishments was found in a 1959 note in which then-Prime Minister Harold Macmillan, in a fit of annoyance, asked a subordinate, “Can nothing be done to suppress or get rid of Mr. Chapman Pincher? I am getting very concerned about how well informed he always seems to be on defence matters.”

Henry Chapman Pincher was born March 29, 1914, in Ambala in India, where his father had been in the British military. After World War I, the family returned to England.

Mr. Pincher studied biology at King’s College in London and, while still a student, published scientific papers on genetics.

After military service, he became the defense, science and medical editor of the Daily Express and later worked for other newspapers.

One of his editors at the Express, he said, suggested that he drop his first name from his byline, saying it would give him a dash of upper-class panache.

Mr. Pincher wrote historical romances, science fiction and espionage novels and several nonfiction books about the world of spies and secrets.

According to British news accounts, Mr. Pincher’s survivors include his third wife, Constance Sylvia Wolstenholme, whom he married in 1965; and two children from a previous marriage.

“The thing he was most proud of,” his son told the Guardian, “was that he never had to retract a story.”

One of Mr. Pincher’s final comments, according to his son, was, “Tell them I’m out of scoops.”