PARTY PIECE gave MI5 total access to the Party organization. Every file contained a statement, handwritten by the recruit, explaining why he or she wished to join the Party, accompanied by full personal details, including detailed descriptions of the circumstances of recruitment, work done for the Party, and contacts in the Party organization. More important than this, the PARTY PIECE material also contained the files of covert members of the CPGB, people who preferred, or whom the Party preferred, to conceal their identities. Most of these covert members were not of the same generation as the classical secret Communists of the 1930s, many of whom had been later recruited for espionage. These were people in the Labor Party, the trade union movement or the Civil Service, or some other branch of government work, who had gone underground largely as a result of the new vetting procedures brought in by the Attlee Government.
In the years after World War II, largely as a result of our alliance with the Soviet Union in the war, the CPGB retained a significant body of support, most importantly in the trade union movement. They were increasingly active in industrial disputes, much to the consternation of Prime Minister Attlee in his later years. In the late 1940s, MI5 began to devote resources in an effort to monitor and neutralize CPGB activity in the trade union movement. By 1955, the time of PARTY PIECE, the CPGB was thoroughly penetrated at almost every level by technical surveillance or informants. Obtaining the PARTY PIECE material, the very heart of the CPGB's administration, was the final proof of MI5's postwar mastery. Ironically, within a year the Soviet Union invaded Hungary, and the Party began its slow decline in popularity.
Once MI5 was in possession of the PARTY PIECE material, the CPGB was never again in a position to seriously threaten the safety of the realm. From then on, MI5 was able to locate every single active Party member, particularly the covert ones, and monitor their activities, preventing them from obtaining access to classified material where the risk arose. The PARTY PIECE material was Y-Boxed, and remained of enormous assistance right up until the early 1970s, especially when the CPGB later began to protest that it had renounced secret membership and was now merely an open party.
I first operated against the CPGB in the late 1950s, when Hugh Winterborn and I installed yet another microphone into its King Street headquarters. The CPGB knew that its building was under constant technical surveillance, and regularly switched the location of important meetings. An agent inside King Street told his F4 controller that Executive Committee discussions had been moved to a small conference room at the far end of the building. There were no windows in the room and we knew from the agent that there was no telephone either, so SF could not solve the problem of providing coverage. Later, in the 1960s, the reason for the lack of a telephone became clear. One of the first things Anthony Blunt had betrayed to the Russians was the existence of SF, immediately after it was first installed in King Street, and they had alerted the Party and instructed them to remove all telephones from sensitive areas. But the Party did not really believe it. They took precautions only for very sensitive matters.
Winterborn and I drove down to King Street in my car and sat outside studying the external walls, trying to decide the best way to attack the target room. Low down on the left-hand side of the street-facing wall was an old coal chute which had been out of use for many years. It seemed to present the best possibility. We checked with the agent where this chute went and were told that it led straight into the conference room. I suggested to Winterborn that we make a false door identical to the one already in the chute, clipping it over the top of the old door with a radio microphone between the two feeding into the keyhole.
Hugh immediately began to make the arrangements. First he designed a new door which could lock against the chute with spring catches.
The door obviously had to be painted the same color as the existing one, which was a heavily weather-beaten brown. We contacted the Building Research Station in Garston and sent them sample flecks of the paint which Hugh removed with a screwdriver one night while casually walking past. They identified the paint for us and acquired some of a similar vintage. Using a blowtorch and a sink of water we were able to simulate a weathering process. I handled the installation of the radio microphone on our door. I used a small plastic audio tube to run from the keyhole in the chute to the microphone, filling the rest of the space with batteries so that the microphone could run without being serviced for up to six months. The receiver was hidden in the telephone footway box at the end of King Street which luckily was just within range of the microphone, and telephone lines relayed the signal back to the seventh floor of Leconfield House.
The most risky part of the operation was fitting the false door on the pavement of King Street It had to be done in full view of the CPGB building, and they were constantly alert to anything suspicious. Hugh Winterborn devised a typically complex plan. He decided to make the installation late on a Saturday night, as theater revelers thronged the streets in Covent Garden. He arranged for all available A2 and F4 officers and their wives to converge on King Street from different directions at a set time. We were all choreographed carefully by Winterborn to arrive in two groups pretending to be much the worse for drink. We met on the pavement and exchanged greetings. Behind the huddle Winterborn dropped down to his knees and began to hand drill four small holes in the wall of the chute, ready to receive the spring catches of our door, using his pocket handkerchief to catch the telltale brick dust. Within a minute our noisy socializing began to wear a little thin, but Winterborn had nerves of steel. He patiently finished the drilling, slipped the false door out from under his coat and clipped it into place.
The operation, known as TIEPIN, worked perfectly as planned and for some months MI5 had full coverage of every important CPGB meeting. But in the end the microphone was detected. A CPGB official happened to settle on our frequency when tuning his radio and a "howl round" alerted him to the presence of a device. The entire building was turned upside down in the search for the bug. Fortunately Hugh Winterborn was living in the flat on the top floor of Leconfield House at the time while his wife was away visiting relatives in Norway. He was alerted as soon as the microphone was detected and went around straightaway, undipped the false door, and brought it back to the office like a trophy of war.
The most extensive microphoning operation Winterborn and I ever undertook was in Lancaster House, the ornate building which hosted the Colonial Conferences of the 1950s and 1960s. As soon as Macmillan became Prime Minister the pace of change in Colonial Affairs became more marked. MI5, which was responsible for security and intelligence-gathering in all Crown Territory, including the Empire, came under increasing pressure to provide intelligence assessments during negotiations toward the various independence settlements. Lancaster House was almost impossible to cover effectively in a piecemeal way. We could never be sure which rooms were going to be used, and this seriously impaired our intelligence-gathering. Winterborn and I proposed that MI5 install a comprehensive microphone system throughout the building which could be used whenever and wherever it was required. The Colonial Office agreed enthusiastically to our request, and Lancaster House was closed for "renovations" for a fortnight while an A2 team moved in. Hugh and I had already studied the room plans with great care and drawn up a circuit diagram specifying the locations of each microphone. We supervised the installation, and throughout the rest of the 1960s and the 1970s the system was used whenever high-level diplomatic negotiations took place in London.