“Because I had been born into the British governing class, because I knew a lot of people of an influential standing, I knew that they would never get too tough with me,” he told the Stasi. “They’d never try to beat me up or knock me around, because if they had been proved wrong afterwards, I could have made a tremendous scandal.”

Mr. Philby, with a note of amusement, described how easy it was for him to steal secret documents. He befriended the archivist at MI6 and bought him drinks, and then he had access to files that were not within his area.

“Every evening I left the office with a big briefcase full of reports which I had written myself, full of files taken out of the actual documents, out of the actual archives,” he said. “I was to hand them to my Soviet contact in the evening. The next morning I would get the file back, the contents having been photographed, and take them back early in the morning and put the files back in their place. That I did regularly, year in, year out.”

The best-known video recording of Mr. Philby is from a news conference in 1955, in his mother’s London apartment, in which he denied being a Communist spy after being dismissed by MI6 but cleared in Parliament by Prime Minister Harold Macmillan.

He was later rehired, and it was not until late 1962 that the British became convinced he was a double agent and sent a new interrogator to meet him in Beirut.