‘They are foolproof provided fools are at the controls. Put a smart crook at the controls and the situation changes very rapidly. He can do a lot of damage, a very great deal.’ He squinted at me through his glasses, looking a trifle unsure about whether he should be telling a confirmed mass-killer like myself information of this nature. He decided to go on, although the expression of doubt remained on his face. ‘All nuclear reactors rely on a delicate balance of rods in their cores, and computers which are monitored by the controllers maintain this balance. If the rods are pushed too far in, the reaction stops completely; if they are pulled too far out, the heat builds up too much, and as the heat builds up, so does the pressure. There are escape valves for when the pressure gets too high, and emergency filtration systems for releasing coolant into the air, but if those escape valves are shut off, and the filtration systems jammed, the containment building’s going to turn into a pressure cooker. The walls of the containment buildings are built strong enough to withstand jumbo jets crashing into them, and to withstand two thousand pounds per square inch of pressure from the inside; but in the event of the safety valves jamming when the reactor is out of control, there could be a build-up of one hundred times that amount within a couple of hours – and the containment isn’t going to hold that. It will either start to crack, or it will just blow to smithereens. Whichever it does, it’s going to release an almighty amount of fallout that would start travelling downwind, and cause serious contamination for a good hundred miles. The average nuclear reactor has several hundred times the radioactive content of, for instance, the Hiroshima bomb.’

‘I thought,’ said Fifeshire, ‘that the British gas-cooled reactors use carbon dioxide as a coolant? Surely carbon dioxide, being lighter than air, would just rise straight into the atmosphere?’

‘The carbon dioxide is lighter than air, but the radioactive materials that it picks up aren’t, and they would start to drop out into the air as it rose. And don’t forget, we don’t just have gas-cooled reactors in Britain now – we have two PWR power stations, each with four pressurized-water reactors. They would send steam pouring out, and that all comes back down to earth.’

Fifeshire blew out another mouthful of smoke and watched it spread across the room, sinking here, rising there, spreading all the time.

‘Wind eddies, swirls, revolves. If you’re smoking your cigar outside, and I’m lying on the ground, with the wind blowing in the right direction, I’ll get a good helping of your smoke. The principal isn’t much different.