Denman's main office was lined with trestle tables running the length of the room. Each table carried mail addressed to different destinations: London letters on one side, Europe on another, and behind the Iron Curtain on a third. Around twenty Post Office technicians worked at these tables opening pieces of mail. They wore rubber gloves so as not to leave fingerprints, and each man had a strong lamp and a steaming kettle beside him. The traditional split-bamboo technique was sometimes used. It was ancient, but still one of the most effective. The split bamboo is inserted into the corner of the envelope, which is held up against a strong light. By turning the bamboo inside the envelope, the letter can be rolled up around the slit and gently pulled out
Where a letter had an ordinary typed address it was sometimes torn open and a new envelope typed in its place. But to the end of my career we were never able to covertly open a letter which had been sealed at each edge with Sellotape. In those cases, MI5 took a decision as to whether to open the letter and destroy it, or send it on in an obviously opened state. Pedal-operated microfilming cameras copied the opened mail and prints were then routinely sent by the case officer in charge of the interception to the Registry for filing.
Denman's proudest memento was a framed letter which hung on the far wall. It was addressed to a prominent Communist Party member whose mail was regularly intercepted. When the letter was opened the Post Office technicians were amused to discover that it was addressed to MI5 and contained a typewritten message, which read: "To MI5, if you steam this open you are dirty buggers." Denman classified it as "obscene post," which meant that legally he had no duty to send it on to the cover address.
In fact, Denman was very particular about warrants. He was prepared to install a tap or intercept an address without a warrant only on the strict understanding that one was obtained as soon as possible. MI5 were, however, allowed to request a form of letter check without a warrant. We could record everything on an envelope, such as its origin and destination and the date it was sent, as long as we did not actually open it. Denman, like everyone in the Post Office who knew of the activity, was terrified in case the Post Office role in telephone and mail intercepts was discovered. They were not so worried about overseas mail, because that could be held up for days at a time without arousing suspicion. But they were always anxious to get domestic mail on its way to the receiver as soon as possible.
Responsibility for warrants lay with the Deputy Director-General of MI5. If an officer wanted a tap or an interception, he had to write out a short case for the DDG, who then approached the Home Office Deputy Secretary responsible for MI5. The Deputy Secretary would advise as to whether the application presented any problem. Once a month the Home Secretary vetted all applications. Like the Post Office, the Home Office was always highly sensitive on the issue of interceptions, and they were always strictly controlled.
As well as St. Paul's, there was also Dollis Hill, the rather ugly Victorian building in North London where the Post Office had its research headquarters in the 1950s. John Taylor ran his small experimental laboratory for MI5 and MI6 in the basement behind a door marked "Post Office Special Investigations Unit Research." The rooms were dark and overcrowded, and thoroughly unsuitable for the work that was being attempted inside.
When I joined MI5, Taylor's laboratory was overrun with work for the Berlin Tunnel Operation. A joint MI6/CIA team had tunneled under the Russian sector of Berlin in February 1955, and placed taps on the central communications of the Soviet Military Command. The actual electrical taps were done by Post Office personnel. Both the CIA and MI6 were reeling under the sheer volume of material being gathered from the Tunnel. So much raw intelligence was flowing out from the East that it was literally swamping the resources available to transcribe and analyze it. MI6 had a special transcription center set up in Earl's Court, but they were still transcribing material seven years later when they discovered that George Blake had betrayed the Tunnel to the Russians from the outset. There were technical problems too, which Taylor was desperately trying to resolve, the principal one being the ingress of moisture into the circuits.
Taylor's laboratory was also busy working on a new modification to SF (Special Facilities), called CABMAN. It was designed to activate a telephone without even entering the premises by radiating the telephone with a powerful radio beam. It worked, but only over short distances.
They were also in the early stages of developing a device called a MOP. A MOP made a cable do two jobs at once - transmit captured sound and receive power. It was in its early stages, but it promised to revolutionize MI6 activity by removing the extra leads which were always likely to betray a covert microphoning operation. I spent a lot of time in my first years in MI5 ensuring the correct specifications for MOP, and it was eventually successfully manufactured at the MI6 factory at Boreham Wood.
Soon after the Philby interview I began to look into ways of improving and modernizing the seventh floor. The method of processing a tap followed a set pattern. A case officer responsible for a tap or microphone provided the Transcription Department with a written brief detailing the sort of intelligence he thought might be obtained from the interception. The transcription staff then scanned the conversation for passages which corresponded to the brief. When I first joined, the taps were normally transferred onto acetate, rather than tape. The acetates were scanned by "dabbing" into the disc at various points to sample the conversation. If anything of relevance was found, the transcribers placed a chalk mark on the appropriate place and worked from the chalk marks. It was an inefficient and time-consuming operation but more efficient than standard tape-recording methods.
Most of these transcribers had been recruited in Kell's day from the emigre communities who fled to Britain at the end of World War I. They had turned the seventh floor into a tiny piece of Tsarist Russia. Most of them were members of the old Russian aristocracy, White Russians who talked with certainty of returning to the lands which had been expropriated after the Revolution. To them the KGB was not the KGB, it was the old Bolshevik Cheka. Most were fiercely religious, and some even installed icons in their rooms. They were famed throughout the office for their tempers. They considered themselves artists and behaved like prima donnas. Hardened case officers seeking clarification of a transcription approached the seventh floor with trepidation in case their request caused offense. The difficult atmosphere was inevitable. For years these women had listened, day after day, hour after hour, to the indecipherable mutterings and labyrinthine conspiracies of Russian diplomats. Spending a lifetime looking for fragments of intelligence among the thousands of hours of worthless conversation (known in the trade as "cabbages and kings") would be enough to turn any mind.