'What can I do for you boys?' he said with the urgent politeness with which a shopkeeper might greet a customer arriving a moment or two before closing time.

'I need advice, Lange.'

'Ah, advice. Everybody wants it: nobody takes it. What can I tell you?'

'Tell me about the Wall.'

'What do you want to know?'

'Escaping. I'm out of touch these days. Bring me up to date.'

He stared at me for a moment as if thinking about my request. 'Forget glasnost,' said Lange. 'If that's what you've come here to ask me. No one's told those frontier guards about glasnost. They are still spending money improving the minefields and barbed wire. Things are still the same over there: they still shoot any poor bastard who looks like he might want to leave their part of town.'

'So I hear,' I said.

'Then where do I start?'

'At the beginning.'

' Berlin Wall. About 100 miles of it surrounds West Berlin. Built Sunday morning August 1961… Hell, Bernard, you were here!'

'That's okay. Just tell me the way you tell the foreign journalists. I need to go through it all again.'

A flicker of a smile acknowledged my gibe. 'Okay. At first the hastily built Wall was a bit ramshackle and it was comparatively easy for someone young, fit and determined to get through.'

'How?'

'I remember the sewers being used. The sewers couldn't be bricked off without a monumental engineering job. One of my boys came through a sewer in Klein-Machnow. A week after the Wall went up. The gooks had used metal fencing so as not to impede the sewage flow. My guys from this side waded through the sewage to cut the grilles with bolt-cutters and got him out. But after that things gradually got tougher. They got sneaky: welded steel grids into position and put alarms and booby-traps down there – put them under the level of the sewage so we couldn't see them. The only escape using the sewers that I heard of in the last few years were both East German sewage workers who had the opportunity to loosen the grid well in advance.'

'So then came the tunnels,' I said.

'No, at first came all the scramble escapes. People using ladders and mattresses to get across places where barbed wire was the main obstacle. And there were desperate people in those buildings right on the border: leaping from upstairs windows and being caught in a Sprungtuch by obliging firemen. It all made great pictures and sold newspapers but it didn't last long.'

'And cars,' said Werner.

'Sure cars: lots of cars – remember that little bubble car… some poor guy squeezed into the gas tank space? But they wised up real fast. And they got rid of any Berlin kids serving as Grenztruppen – too soft they said – and brought some real hard-nosed bastards from the provinces, trigger-happy country boys who didn't like Berliners anyway. They soon made that sort of gimmick impossible.'

'False papers?'

'You must know more about that than I do,' said Lange. 'I remember a few individuals getting through on all kinds of Rube Goldberg devices. You British have double passports for married couples and that provided some opportunities for amateur label fakers, until the gooks over there started stamping "travelling alone" on the papers and keeping a photo of people who went through the control to prevent the wrong one from using the papers to come back.'

'People escaped in gliders, hang-gliders, microlites and even hot-air balloons,' said Werner helpfully. He was looking at me with some curiosity, trying to guess why I'd got Lange started on one of his favourite topics.

'Oh, sure,' said Lange. 'No end of lunatic contraptions and some of them worked. But only the really cheap ideas were safe and reliable.'

'Cheap?' I said. I hadn't heard this theory before.

'The more money that went into an escape the greater the number of people involved in it, and so the greater the risk. One way to defray the cost was to sell it to newspapers, magazines or TV stations. You could sometimes raise the money that way but it always meant having cameramen hanging around on street corners or leaning out of upstairs windows. Some of those young reporters didn't know their ass from their elbow. The pros would steer clear of any escapes the media were involved with.'

'The tunnels were the best,' pronounced Werner, who'd become interested in Lange's lecture despite himself.

'Until the DDR made the 100-metre restricted area, all along their side of the Wall, tunnels were okay. But after that it was a long way to go, and you needed ventilation and engineers who knew what they were doing. And they had to dig out a lot of earth. They couldn't take too long completing the job or the word would get out. So tunnels needed two, sometimes three, dozen diggers and earth-movers. A lot of bags to fill; a lot of fetching and carrying. So you're asking too many people to keep their mouths shut. You trust a secret to that many people and, on the law of averages, at least one of them is going to gossip about it. And Berliners like to gossip.'

I said nothing. Mrs Koby came in with the tea. Upon the tray there was a silver teapot and four blue cups and saucers with gilt rims. They might have been heirlooms or a job lot from the flea-market at the old Tauentzienstrasse S-Bahn station. Gerda poured out the tea and passed round the sugar and the little blue plate with four chocolate 'cigarettes'. Lange got a refill of his plum wine: he preferred that. He took a swig of it and wiped his mouth with a big wine-stained handkerchief.

Lange hadn't stopped: he was just getting going. 'Over there, the Wall had become big business. There was a department of highly paid bureaucrats just to administer it. You know how it is: give a bureaucrat a clapboard doghouse to look after and you end up with a luxury zoo complete with an administration office block. So the Wall kept getting bigger and better and more and more men were assigned to it. Men to guard it, men to survey it and repair it, men to write reports about it, reports that came complete with cost-estimates, photos, plans and diagrams. And not just guards: architects, draftsmen, surveyors and all the infra-structure of offices, with clerks who have to have pension schemes and all the rest of it.'

'You make your point, Lange,' I said.

He gave no sign of having heard. He poured more wine and drank it. It smelled syrupy, like some fancy sort of cough medicine. I was glad to be allergic to it. He said, 'Wasteful, yes, but the Wall got to be more and more formidable every week.'

'More tea, Bernard,' said Gerda Koby. 'It's such a long time since we last saw you.'

If Gerda thought that might be enough to change the subject she was very much mistaken. Lange said, 'Frank Harrington sent agents in, and brought them out, by the U-Bahn system. I'm not sure how he worked it: they say he dug some kind of little connecting tunnel from one track to the next so he could get out in Stadtmitte where the West trains pass under the East Sector. That was very clever of Frank,' said Lange, who was not renowned for his praise of anything the Department did.

'Yes, Frank is clever,' I said. He looked at me and nodded. He seemed to know that Frank had deposited me into the East by means of that very tunnel.

'Trouble came when the gooks got wind of it. They staked it out and dumped a pineapple down the manhole just as two of Frank's people were getting ready to climb out of it. The dispatching officer was blown off his feet… and he was two hundred yards along the tunnel! Frank wasn't around: he was apple-polishing in London at the time, telling everyone about the coming knighthood that he never got.'

I wasn't going to talk about Frank Harrington; not to Lange I wasn't. 'So the diplomatic cars are the only way,' I said.

'For a time that was true,' said Lange with a wintry smile. 'I could tell you of African diplomats who put a lot of money into their pockets at ten thousand dollars a trip with an escapee in the trunk. But a couple of years ago they stopped a big black Mercedes with diplomatic plates at Checkpoint Charlie and fumigated it on account of what was described as "an outbreak of cattle disease". Whatever they used to fumigate that car put paid to a 32-year-old crane operator from Rostock who was locked in the trunk. They say his relatives in Toronto, Canada, had paid for the escape.'