I pulled out my propelling pencil, pushed the tip in and spoke into the clip. ‘She’s coming out.’ I pushed the button a second time, which switched it onto the receiving cycle and walked over to the window. A couple of minutes passed and there was no sign of Whalley. I figured he must have gone down into the car park, and if he had I wouldn’t see him come out from here, since the car park entrance was at the back of the building. I held the pointed end of the pencil up to my ear. It contained a tiny directional speaker, through which, if pointed at my ear, I could hear perfectly clearly, although someone standing right beside me would not hear a thing.

Another minute passed, then a voice came out of the pencil.

‘This is Sheila. We’ve got her.’

It was our practice to code name both the person being tailed, and the cars tailing, with girls’ names. The names of the three cars today were Sheila, Mavis and Ethel. My name for today was Carol.

‘Stay with her, Sheila,’ I said, ‘I’m coming out too.’

I left the building by the front entrance, turned left and walked up to a grey Cortina that was parked on a jammed meter. It was one of five different cars that were parked on this meter on a daily rotation; I had keys to all five. I started the engine, then pushed into my ear a device that looked like a miniature hearing aid, but was a radio receiver tuned in to the frequency of the three surveillance cars. I could have tuned in to Whalley as well, had I wanted, but I didn’t think he would have a great deal to say to himself whilst driving along on his own. I clicked the top of my propelling pencil and spoke into it. ‘This is Carol. Where’s the party?’

‘At the fairground. Looks like we’re going on the helter skelter.’

The fairground was code for Hyde Park Corner and the helter skelter was Park Lane. It was highly unlikely that Whalley was eavesdropping on us, but in surveillance we avoid taking risks. Although we changed our frequency daily, and sometimes more often than that, there was always the danger he could stumble across it accidentally, and if he heard places mentioned where he was actually driving at the time, it wouldn’t take him long to put two and two together. So, like the police, we had an elaborate language for tailing, complete with its own vocabulary and key-place nicknames.

I caught up with Ethel, the back-marker of the cars, going around Swiss Cottage; Ethel was a brown Morris Ital. I overtook Ethel and sat behind Mavis, a mustard Chrysler Horizon. That’s one thing about the security services – they always buy British cars. Anyone worried about being tailed by MI5 can relax if he sees foreign cars behind him.