‘In the old days, the main job was to watch out for rats,’ said Headon. ‘That was the code word for hostile aircraft. A lot of men liked that part of the job, distinguishing friend from foe, a bomber from a fighter. Losing that aircraft recognition role was very disappointing. Quite a few observers left the ROC then. But we were still serving our country, weren’t we? Well, that’s what we thought.’

Two miles out of town they turned and headed uphill.

‘Some people didn’t want underground bunkers on their land,’ said Headon. ‘It was usually the bigger landowners who refused. Farmers were a bit more co-operative. There was a little bit of money to be made out of it, but not much.’

‘And Edendale?’

‘Edendale was a master post. It had the radio set.’

Cooper knew that Headon and Falconer were both enthusiasts, the kind who wanted to talk about their obsession. The trick was to filter out the information from the mass of reminiscence. But he was glad of the excuse to get out of the way, to interest himself in something else and let Diane Fry bring her case to a conclusion back at West Street. She didn’t need him getting under her feet. In fact, she didn’t need him at all. She’d said so herself.

‘The ROC was stood down in 1991, you said, David?’

‘That’s when the last posts were closed.’

‘They thought they didn’t need the Observer Corps quite so much by then?’

‘Right.’

Following Headon’s directions, Cooper swung the Toyota on to a narrow single-track lane that ran uphill between high dry-stone walls. Throughout the area, wallers were hard at work repairing the ravages of the Peak District winter. They passed one waller who had an old DAF towing a small caravan. If you had a long job to do, it was easier if you could live on site, he supposed.

‘But do you all still keep in touch?’

‘Some of us,’ said Headon. ‘There’s an association, you see. We have a newsletter, a benevolent fund, social get-togethers occasionally. I think there’s even a forum on the internet.’

‘So what are these underground posts like?’

‘Pretty basic. There’s a twenty-foot vertical ladder leading down to an underground chamber, seven feet wide and sixteen feet long. That housed the observers, their bunk beds, generators, the operations desk, other equipment. Conditions were very primitive.’

‘No running water, or mains electricity,’ chipped in Falconer.

‘Yes, and the only communication with the outside world was a Tele-Talk device connected to Group HQ, and of course the warning receiver. You needed dedicated people, prepared to lock themselves away in those conditions.’

‘Let’s be honest. We were a bit out of the ordinary,’ said Falconer. ‘The general public reaction was “If the bomb drops, we’re all going to die anyway, so why bother?”’

Cooper looked at him through his rear-view mirror. He was about the same age as David Headon. They were two old men, living on their memories. The further in your past a period was, the more it started to seem like the best days of your life.