If, like me, you’ve spent two years as a PCSO and another two as a PC patrolling central London in the late evenings, you become something of a connoisseur of street violence. You learn to differentiate the bantam posturing of drunks or the shrieking huddle of a girls-night-out gone south from the ugly shoving of a steaming gang and the meaty, strangely quiet, crunch that indicates an intense desire by one human being to do your actual bodily harm to another.

I heard a grunt, a smack, a whimper and before I thought about it I had my extendable baton out and was across the road and heading for the shadows around the alley opposite the market. There were two of them, bulky shapes in cold weather jackets, laying into a third person who was hunched up in the snow.

‘Oi,’ I shouted. ‘Police! What do you think you’re doing?’ It’s traditional.

They turned and stared as I ran at them – there was one big one and one skinny, as is also traditional. I recognised the skinny one. It was Kevin bloody Nolan. He would have bolted, except that his big friend was made of sterner stuff.

The thing about being the police is that to do the job properly part of you has to enjoy getting stuck in. And the thing about members of the public, like the big idiot with Kevin Nolan who started squaring up to me, is that they expect there to be at least some kind of ritual exchange of insults before you get down to it. Something I had no intention of indulging in.

The big one had just enough time to register that I wasn’t going to stop when I drove my shoulder into his chest. He staggered backwards and tripped over the cowering man behind him. As he went down, bellowing, I swiped Kevin bloody Nolan’s thigh with my baton hard enough to give him a dead leg. Then I just reached out and shoved him off his feet.

‘You bastard,’ said the big man as he tried to get up.

‘Stay down or I’ll break your fucking arms,’ I said and then thought. Shit, I only have one set of handcuffs. Luckily the big man lay down again.

‘Are you really the police?’ he asked almost plaintively.

‘Ask your mate Kevin,’ I said.

The big man sighed. ‘You stupid cunt,’ he said, but he was talking to Kevin. ‘You utter, utter moron.’

‘I didn’t know he was going to be here,’ said Kevin.

‘Just keep your gob shut,’ said the big man.

I pushed his legs off the figure in the snow who rolled over and grinned up at me – it was Zach. What a surprise.

‘You know I was really hoping for a St Bernard,’ he said as he sat up.

‘But what you’re asking for is a smacking,’ I said.