(Credit: Getty images) 

He was pushing her around. Right in front of me. There on the pavement. At rush-hour. In broad daylight. He — stocky, crew cut — was shoving her forward violently, then yanking her back, in a series of frenetic, push-pull movements. She was shrieking, he shouting in a language I couldn't identify (which hardly narrows it down). 

I was hurrying home from Shepherd's Bush station, across one side of the triangle which is the Green, already late for supper (when we're hosting, my wife gets strangely cross if I arrive after our guests).

But here was this.  

The man's aggression escalating, I decided there was nothing for it. I tried to squeeze in between them to separate the pair, to   prize them apart. And it worked: immediately his fury was transferred on to me. With one hand he grabbed my collar, while the other he seemed to be winding up for a punch. We locked eyes: I could see they were silky but wild too, under the influence. 

I tried to keep my body and head low, tucked in tight, to protect against blows. 

He wheeled me round in a kind of mad balletic dance. I glanced round desperately for help. The crowd stepped aside to avoid us, like excrement smeared on the concrete, passers-by rather than onlookers —until one young black man stopped, took his headphones out of his ears, and promptly pulled me away from the clutches of my opponent.

But this was not the eventuality I had intended. Because rather than running for cover, the woman had stood frozen to the spot, looking on, as Gertrude says of Ophelia, "as one incapable of her own distress, like a creature native and indued unto that element". 

And then an older woman bounded up to me: "I saw everything! There are police! Just up ahead!"

So I stepped into the street and sprinted, along the kerb and against the traffic, knocking a beer out of someone's hand as I ran, sending it to the ground fizzing and frothing. I finally found the pair of policemen. 

"There's a man!" — breathless — "a man assaulting a woman!"

The three of us ran back in the direction I had come from.

First we found the woman. Except that now she was alone. "That's her!" I cried. Instantly shedding a third of our infantry, two of us continued on, myself and the rotund, mid-fifties silver fox I'll call PC Lightning Strike.