We drank beer. I preferred an Indian meal partly because no one was expected to drink anything strong with a curry. This wasn't going to be the right time to get Stinnes boozed to the point of indiscretion. And it wasn't going to be the right expense account either. At this first outing, Stinnes would be wary of such tactics, but his first sip of the fizzy water that the British call lager allayed all such fears. He pursed his lips in distaste, but didn't complain about the watery beer or anything else.

The decor was typical of such places: red-flock wallpaper and a dark-blue ceiling painted with stars. But the food was good enough, flavoured with ginger and paprika and the milder spices. Erich Stinnes seemed to enjoy it. He sat against the wall with Gloria next to him, and although he supplied his due amount of small talk, his eyes moved constantly, looking to see whether any of the other customers, or even staff, looked like departmental employees. That's the way Moscow would have done it; they always have watchers to watch the watchers.

We had been talking about books. 'Erich likes reading the Bible,' I announced for no real reason other than to keep the conversation going.

'Is that true?' she said, turning to Erich Stinnes.

Before he could answer, I explained, 'He was with Section 44 back in the old days.'

'Do you know what that is?' he asked her.

'The KGB's Religious Affairs Bureau,' she said. It wasn't easy to catch her out; she knew her way around the files. 'But I don't know exactly what they do.'

'I'll tell you something they do,' I said to her, ignoring the presence of Stinnes for a moment. They desecrate graves and spray swastikas on the walls of synagogues in NATO countries so that the Western press can make headlines speculating about the latest upsurge of neo-Nazi activity and get a few extra votes for the left-wingers.'

I watched Stinnes, wondering if he'd deny such outrages. 'Sometimes,' he said gravely. 'Sometimes.'

I'd finished eating, but now she picked up a crisp papadom I'd not eaten and nibbled at it. 'Do you mean you've become a dedicated Christian?'

'I'm not a dedicated anything,' said Stinnes. 'But one day I will write a book comparing the medieval Church to applied Marxist-Leninism.'

This was just the sort of talk she liked: an intellectual discussion, not the bourgeois chitchat, office gossip, and warmed-up chunks of The Economist that I served her. 'For instance?' she said. She furrowed her brow; she looked very young and very beautiful in the dim restaurant lighting, or was that British lager stronger than I thought.

'The medieval Church and the Communist state share four basic dictums,' he said. 'First and foremost comes the instruction to seek the life of the spirit: seek pure Marxism. Don't waste your efforts on other trivial things. Gain is avarice, love is lust, beauty is vanity.' He looked round at us. 'Two: Communists are urged to give service to the state, as Christians must give it to the Church – in a spirit of humility and devotion, not in order to serve themselves or to become a success. Ambition is bad: it is the result of sinful pride…'

'But you haven't…' said Gloria.

'Let me go on,' said Stinnes quietly. He was enjoying himself. I think it was the first time I'd seen him looking really happy. 'Three: both Church and Marx renounce money. Investment and interest payments are singled out as the worst of evils. Four, and this is the most important similarity, there is the way in which the Christian faithful are urged to deny themselves all the pleasures of this world to get their reward in paradise after they die.'

'And Communists?' she asked.

He smiled a hard close-lipped smile. 'If they work hard and deny themselves the pleasures of this world, then after they die their children will grow up in paradise,' said Stinnes. He smiled again.

'Very good,' said Gloria admiringly. There wasn't much left on the plates or dishes that covered the table. I'd already had enough to eat – a little curry goes a long way with me – so she picked up the dish of chicken korma and divided the last of it onto their two plates.

Stinnes took the dishes of the rice and the eggplant and, when I declined, divided the food between them.

'You missed out number five,' I said, while they were tucking into their final helpings. Both of them looked at me as if they'd forgotten I was there with them. 'Victory over the flesh. Both Church and Communist state preach that.'

I was serious, but Gloria dismissed it. 'Very funny,' she said. She wiped her lips with the napkin. To Stinnes she said, 'Was the Church very opposed to capitalism? I know it objected to loaning money and collecting interest, but it wasn't opposed to trading.'

'You're wrong,' said Stinnes. The medieval Church preached against any sort of free competition. All craftsmen were forbidden to improve tools or change their methods lest they take advantage of their neighbours. They were forbidden to undersell; goods had to be offered at a fixed price. And the Church objected to advertising, especially if any trader compared his goods with inferior goods offered by another trader at the same price.'

'It sounds familiar,' said Gloria. 'Doesn't it, Bernard?' she asked, politely drawing me into the conversation as she looked into a tiny handbag-mirror to see that her lips were wiped clean of curry.

'Yes,' I said. 'Homo mercator vix aut numquam potest Deo placare – a man who is a merchant will never be able to please God – or please the Party Congress. Or please the Trades Union Congress either.'

'Poor merchants,' said Gloria.

'Yes,' said Stinnes.

The waiter came over to our table and began clearing the dishes away. He offered us a selection of those very sweet Indian-style desserts, but no one wanted anything but coffee.

Stinnes waited until the table was completely cleared. It was as if this action prompted him to change the conversation: he leaned forward, arms on the table, and said, 'You were asking about code words… radio codes… two names for one agent.' He stopped there to give me time to shut him up if I didn't want Gloria to hear the rest of the conversation.

I told him to go on.

'I said it was impossible. Or at least unprecedented. But I've been thinking about it since then…'

'And?' I said after a long pause during which the waiter put the coffee on the table.

'I told you it was nonsense, but now I think you may be correct. There was a line of intelligence material that I was not permitted to see. It was handled by our radio room, but it went directly to Moscow. None of my staff ever saw it.'

'Was that unusual?' I asked.

'Very unusual, but there seemed no reason to think that we were missing anything very good. I thought it was some Moscow deskman trying to make a name for himself by working on one narrow field of interest. Senior staff in Moscow do that sometimes; then suddenly – choosing their moment carefully – they produce a very thick file of new material and before the cheers die down they get the promotion they've had their eye on.'

'How did you find out about it?'

'It was kept separate, but it wasn't given any special high security rating. That might have been a very cunning idea – it didn't attract so much attention like that. People handling it would just have thought it applied to some boring technical file. How did I come across it? It came onto my desk by accident. It was the second of February of last year. I remember the date because it was my son's birthday. The decoded transcripts were put on my desk with a pile of other material. I looked through it to see what was there and found this stuff with an agent name I didn't recognize but a London coding. I thought it must be a mistake. I thought a typing error had given it the five-letter group for London. It's not often that the typists there make such an error, but it's not unknown. It was only last week that I remembered it in the light of what you were asking me about agents with two code names. Any use to you?'