The young woman in the wheelchair gave us a demonstration. With the fingers on her left hand spread wide she mimed pulling a man’s head to one side. With the knife in her right hand she stabbed the point sideways and then quickly pushed it forward.

‘Punch and pull,’ she said. ‘Punch the tip of the knife through the side of the neck and then pull the blade out of the front. You can’t patch that up with a couple of stitches and some Nurofen Plus. Most people who want to cut a throat start on the outside. They hack and saw and chop.’

She mimed hacking and sawing and chopping.

‘That’s all right if you want to hurt their feelings,’ she said. ‘That’s all right if you want to put a crimp in their day. But not if you want to be certain of killing them.’

‘The punch and pull,’ Mallory said. ‘It cuts the windpipe and then you have a good chance of cutting the carotid arteries.’

‘More than a good chance,’ Carol said. ‘That move is called the carotid thrust. Cutting the carotid arteries is the whole point, sir. If the shock doesn’t immediately kill them, then they die because the carotids have been severed and there’s no blood being pumped from the heart to the brain.’

‘How long?’ I asked.

‘Brain-dead immediately,’ she said. ‘Unconscious in five seconds and dead in twelve seconds.’

‘And when did they stop making these knives?’

‘They’ve never stopped making these knives. It’s been evolving for almost a hundred years. There’s a contemporary version used by the Special Forces – the UK-SFK. It’s the greatest combat knife ever invented.’ She looked at Mallory, and I wondered how they knew each other. ‘And now Bob the Butcher’s got one.’

Mallory smiled. ‘We don’t know if it’s Bob,’ he said. ‘What we do know is that it’s someone with training who has access to specialist weapons.’ He looked at me. ‘Presumably you can get a Fairbairn-Sykes online?’

‘You can buy anything online,’ I said.

‘Apart from training and knowledge and the expertise you would need to execute the carotid thrust,’ Carol said. ‘That takes years to accumulate. And there’s something else.’

We watched her feel the weight of the Fairbairn-Sykes fighting knife.

‘To kill someone with one of these – to stick the stabbing point in the side of their neck and then pull it clean out the front . . .’ She paused and looked up at Mallory from her wheelchair. ‘You would have to really hate their guts, sir.’

I was in the ring and my legs were gone.