Lunch with a Minister President, coffee with a city mayor — on such occasions not every word is carefully weighed. What relations do leading politicians have to one another . . . ? When, for example, after a session at a Party conference, Schmidt, Wehner, and Brandt visited a Weinstube and went on talking - Guillaume would be at the next table . . . In the car after long sessions of the Party Executive, when Brandt gave vent to 'expressions of displeasure', or 'characterised' somebody . . . When the SPD chiefs talked over a cup of coffee or - at the end of the day - over something stronger, about who was going to be renominated or not and where . . . He could catch the nuances of what was said, and hear confidential briefings to journalists on matters that might later make the headlines. He knew much more than any state secret - he knew about the moods, connections, and developments that could lead to the decisions taken later.

As Bahr said in evidence: 'He was always there, but people weren't aware of him.' Wilke recalled him as always wanting to be in on everything, whether it concerned him or not. Guillaume himself said in his interview with Knopp that he couldn't remember what he'd passed on, but agreed that it included everything he could lay his hands on about the negotiations with Moscow and East Berlin. Stephan Konopatzky, a researcher working on the Stasi files now held in a massive archive in Berlin, can find relatively little information credited to XV/19142/60 and XV/11694/60, aka Hansen and Heinze, aka Günter and Christel Guillaume, and less still that was regarded as of any great value. He concedes that Guillaume's reports may, because of their importance and sensitivity, have been handled by some special channel as yet unexplored in the archive, but thinks it more likely that he was being used very cautiously to protect his unique position. When one thinks of all those monthly debriefings by Arno aka Franz, though . . . What happened to everything that was said? Was it the supportive Arno who thought it wasn't worth passing on?

If Wolf is telling the truth in his memoirs he must have received much more material than the files reveal. He says that before Brandt's visit to Erfurt in March 1970 - i.e., even at the very beginning of Guillaume's employment in the Chancellor's office, when he was still concerned with nothing more than trade union liaison - he 'gained access to some of the West German plans, which, combined with information from other sources, gave us a clearer idea of Brandt's intentions and fears'. He also says that Guillaume's 'real importance for us in East Berlin lay in his political instincts. Through Guillaume's judgements we were able to conclude sooner rather than later that Brandt's new Ostpolitik, while still riven with contradictions, marked a genuine change of course in West German foreign policy. As such, his work actually aided détente by giving us the confidence to place our trust in the intentions of Brandt and his allies.'