It was a slim folder: as well as a transcript of the interview with Slavin in Russian and an English translation of the same, it contained a page of notes by the Chief of Station, Manning, and two grainy, passport-sized photographs that had been taken at some point in the previous two years as part of the station’s routine surveillance of foreign diplomatic staff. It had a very restricted distribution: just Chief and Heads of Section.

It took me a good ten minutes to get through it. I found that I desperately wanted a cigarette, but as there was nothing more certain to get Chief’s dander up than that, I made do with drumming my hands on the arm of the chair.

‘High stakes,’ he muttered, tapping his glass with his fingers.

That was an understatement. Slavin claimed to be a colonel in the KGB and was asking to be smuggled out of Nigeria to a new home in England. In return, he was promising to reveal information about a British agent who had been recruited by Moscow in 1945.

Since Burgess and Maclean had fled to Moscow in ’51, several Soviet agents had been uncovered in the Service, Five and elsewhere. Philby had been the biggest blow - he had been tipped by many for the top. In the six years since his disappearance, the Service had become almost paralysed by the fear that other traitors remained undetected. I’d lost count of the number of officers whose pasts had been put under the microscope; I had even faced questioning myself.

‘Has Henry seen this yet, sir?’ I asked. Henry Pritchard headed up Africa Section; as Slavin was in Nigeria, he would be heavily involved.

Chief nodded. ‘I had it hand-delivered to the homes of all Heads of Section a few hours ago, apart from Edmund, who’s still away - his went to Smale instead. Because you and Henry will be taking the lead on this, I attached invitations to your copies asking you to come round this evening. Station 12 told me you’d been out when they called round, which is why I rang you up myself.’

Station 12 was the messenger service. ‘I see,’ I said. ‘Sorry about that - I was at a concert for most of the afternoon. Was Henry not in either, then?’

He shook his head briskly. ‘No, he got it. I scheduled him for a bit later, though, because I wanted to talk it through with you first. See what you made of it.’

I stood up and walked over to the fireplace, trying to think of a suitable answer.

‘Could Slavin be a plant?’ I asked, but when I turned round I saw he was already shaking his head. It surprised me he felt so certain: several recent defectors were suspected of being Trojan horses, sent over by Moscow to make outrageous allegations so the Service would chase its own tail.