But while RAFTER proved our Watcher communications were a major source of intelligence for the Russians, there was still the question of the missile spy, Linney. Obviously, the investigation of Linney had to be done in such a way that our Watcher radios would not give away the operation. I decided that since radio silence was unrealistic, the best solution was to drastically change the frequencies of the vehicles assigned to the operation. I went to see the Ministry of Defense and asked to pirate one of their military frequencies, seventy megacycles away from the current Watcher frequency, so that the Linney vehicle transmissions would melt into the mass of other military traffic on nearby wavebands. But first I had to install new crystals in the Watcher radio sets so that they could operate on the new frequency. Every communications radio contains a crystal which controls the frequency at which it can receive or transmit. Rather than risk handling this through MI5 channels, I paid a private visit to my old colleague R.J. Kemp, the Marconi Chief of Research, and asked him if he would produce the new crystals for me in the Great Baddow Laboratory. I gave him a sample crystal so he could build one of the correct shape, and stressed that the new frequency should be held only by him and his immediate assistant. As an additional security precaution, we decided to mark the new crystals with an entirely different frequency from the actual one used. Within three weeks Kemp had produced enough crystals for a dozen transmitter and receiver units, and they were installed by the MI5 engineers who normally handled Watcher radios, so as not to raise suspicions.
The details of this operation, code-named LOVEBIRD, were severely restricted inside MI5. Only Winterborn and I knew the correct frequency and none of the new radios were used within range of the Soviet Embassy. The Consulate receiver was continuously monitored using RAFTER, so that we could record how the Russians behaved during the operation against Linney. D Branch had already extensively analyzed the movements of Linney and his controller, Pribyl. By comparing the two, they discovered that their regular meet was on the South Downs near Brighton. We arranged with Special Branch to arrest Linney and Pribyl in the act of passing over secret material at their next rendezvous.
Linney was followed to the meeting place by Watchers equipped with the new frequency. He waited for two hours and then went back home. Pribyl, meanwhile, remained in London. Subsequently, Linney was interrogated, and unexpectedly confessed. He was sentenced to fourteen years imprisonment.
On the face of it, the case had been concluded successfully. But one detail troubled Winterborn, me, and the D Branch officers in charge of the case. Why had Pribyl missed his meeting? There were many reasons which might explain his failure to show up. He had not missed any other meets. But if he had learned of the planned arrest, it could not have been from the Watcher radios. It could only have been as a result of a tip-off from a human source.
I decided to conduct another experiment to resolve the question of whether or not there was a two-legged source operating for the Russians in conjunction with the intelligence they were obtaining from our Watcher radios. I arranged to change all Watcher radio crystals simultaneously while monitoring, by means of RAFTER, the Russian receiver, to see precisely what they did. It was impossible to make a change on this scale without recording the details inside Leconfield House, but I was confident that none of the Watchers would learn of the plan in advance.
We began RAFTER on the Russian receiver on a Monday morning, and chased Russian diplomats normally on our usual frequency. On the Tuesday and Wednesday we closed down all Watcher operations entirely while we switched the crystals. The Watcher force was told that the frequency was being moved up two megacycles, when in fact it was being moved down two instead. We opened up again on Thursday, chasing diplomats normally on our new frequency. We watched the RAFTER readings carefully for any signs that the Russians were searching for our new frequency in the area where we had indicated to the Watchers that it was being relocated. They did appear to check their equipment, as if it was faulty, but remained on the old frequency until the end of the week.
When we opened up again on Monday morning, everything had changed. A Russian receiver was already listening on the new frequency, but from inside the Embassy in Kensington Park Gardens, rather than from the Consulate. We were faced with another riddle. This new receiver had either searched for the new Watcher frequency the previous week, undetected by us as we concentrated on the Consulate, or the Russians had been tipped off to the new frequency during the weekend. It is unlikely that we would have missed the Russians lining up another receiver on the new frequency the previous week.
I discussed the whole investigation at length with Courtney Young, the head of Russian Counterespionage, and we decided to try one more experiment. If there was a human leak, we all assumed that it had to be among the Watcher or peripheral support services. So we decided to feed what is known in the business as a "barium meal", in other words, offer a bait of sufficiently important intelligence that the two-legged source, if he existed, would have to relay it back to the Russians.
Courtney Young had a double agent case running. The agent, code named Morrow, was in contact with the Russian Naval Attache, Lieutenant Commander Lulakov. We decided on a straightforward plan. We briefed the Watchers about the Morrow case as if he were a genuine spy. They were told that the following day Special Branch had been instructed to arrest Morrow in the process of handing over secret documents to Lulakov at a meeting in Hampstead. Full Watcher surveillance of both Morrow and Lulakov was required. If there was a traitor inside the Watcher service, we assumed he would alert the Russians, who would either fail to turn up for the meeting or try to warn Morrow in some way.
In fact, Lulakov turned up for the meeting right on schedule, got into Morrow's car in a quiet street near Hampstead Heath, and swiftly exchanged packages with him. Both men were promptly arrested. Lulakov established his diplomatic credentials and was released, and left the country soon afterward. The charges against Morrow were quietly dropped.
At first sight it seemed as if the Lulakov/Morrow affair proved there was no human penetration. But as with every previous experiment, there were worrying inconsistencies. Lulakov was known from previous surveillance to be infinitely patient in his preparations for meetings. On previous occasions he had taken hours to wend his way around London, by taxi, by bus, in and out of tubes and shops, before finally making his rendezvous with Morrow. On this occasion, he simply left his office, hailed a taxi, and went straight to the meeting. The handover even took place with the car's interior light on. To anyone with a close knowledge of the Russian Intelligence Service, these were inexplicable deviations from their normal tradecraft.
At the end of 1958 I composed a long report on the whole investigation into the Tisler allegations and sent it to Hollis. I went through the items Tisler had learned from his garrulous friend Colonel Pribyl and gave Hollis my assessment of how the Russians might have learned of them.