Toad had always been a pain to the lads on the squadron, but over the past few weeks, since he’d been posted to the States for a course in nuclear technology, he’d faded into the distance, as it were, and people had stopped beefing about him. It wasn’t his fault that he was ugly, with oily skin and protuberant eyes; what bugged us was that he seemed to have no personality, and never got on with any of the guys. He’d go about with a smarmy smile on his face, but there was no warmth in it, and after a while you came to realise that he was wrapped up in his own affairs. At the same time, he was a real crawler, who’d lick up to anyone if he thought he could gain something from doing so.

How he had ever made it into the Regiment I could never understand. He had come from an unusual source – the Royal Engineers – where he’d worked in bomb-disposal; he was fascinated by explosives – obsessed, almost – and he spent hours tinkering with time-fuses and remote-firing gadgets.

He’d never tell you what he was doing, or have any real crack with the lads. He’d associate with the cooks and drivers rather than with the rest of us. It was no accident that he’d ended up as an instructor on the lock-picking wing, in a dim little world of his own. I know that all SAS guys, myself included, are loners to some extent; but at the same time everyone has to muck in, and Toad never did.

The idea of having to live at close quarters with him in the camp at Balashika was a fucking wind-up. In fact I found the whole scenario a nightmare.

I’d always hated the idea of nuclear weapons because they’re bound to kill thousands of innocent civilians, including any number of children – people who have no idea of what’s going on. My career in the SAS has always emphasised the need for precision: what you might call ‘economy of violence’. People imagine that guys in the Regiment have a cold-blooded, murderous outlook, and regard anybody as a potential target. It isn’t like that. All our training is directed to making surgically accurate strikes on targets that have been properly identified.

For the moment, all I could do was grasp at straws. ‘This tunnel under the river,’ I said. ‘How do we know it’s still open?’

Laidlaw checked his notes, gave a half-smile, and replied, ‘It was open on the fourth of April this year, and we have no reason to believe the situation’s changed.’

‘That means someone’s been down it. If access is that easy, how do we know that the KGB or some other security organisation isn’t sitting in there, waiting for us to arrive?’