‘Bravo, that man! Yes, someone discovered that the GRU had recruited a British agent in Germany at the end of the war and given him the code-name Radnya. They didn’t have my real name, but it was enough. They stored away this information - perhaps they had an inkling that the KI wouldn’t last long. Then, a couple of decades later, as this same fellow sat at the head of some nasty little division of the KGB, he decided that Radnya would make the perfect ingredient for a grand plot against his counterparts in London.’

So I had been right about Slavin being a plant - albeit a very unusual one. Plants had to have a few secrets to hand over or nobody would believe they were genuine defectors. But that information couldn’t be too valuable, or it would defeat the purpose. So you gave them lots of pieces of genuine but not very important information that you knew or suspected the other side already had. Barium, we called it: chicken-feed. But it had got trickier. With the paranoia over plants, all would-be defectors had come under pressure to produce much more than barium. The KGB officer handling Slavin had calculated that the details about a double being recruited in the British Zone in 1945 would be enough for the Service to unmask Radnya’s identity on their own steam, thereby cementing Slavin’s credentials and simultaneously sinking the British into a morass of recriminations over yet another traitor in their ranks. Slavin would then have been able to concoct the most outrageous untruths and have everyone hanging on his every word. At the same time, a body blow would have been dealt to the KGB’s old rivals, the GRU, who wouldn’t have known what had hit them.

It was a brilliant ploy. The only problem with it had been ... me. The KGB hadn’t known that the GRU had, in fact, recruited two British double agents in the same part of Germany at the end of the war, and that both of them - the Russian practice being not to tell agents their own code-names - would presume they were under threat of imminent exposure.

‘Where does the PM come into this?’ I asked.

‘Ah, that,’ said Pritchard, making it sound like a trifling affair. ‘It’s a long story.’

‘We have time,’ I said.

He smiled. I didn’t like the smile, and it set alarm bells off in my head.

‘Anna’s here, isn’t she?’

‘No, Paul. Please let go of that idea. I told you: Anna died a long time ago.’

I could sense a false note somewhere. The eyes. His eyes didn’t move - they were fixed on me. Because he was fighting the urge to look elsewhere. The window? Was it my imagination or was there some noise coming from that direction? What was it - cheering?