Kiddie is lying on the ground behind the bench... Lemmy is thundering up the platform, purple in the face. The ground trembles beneath my feet

Back on the trains again. Willesden Junction station, to be precise. A lovely Saturday afternoon, sometime between tea and the yardarm. Shouts and strains of "La Macarena" float across the dusty air from the back garden of a terrace on the far side of the railway tracks. A dozen people are scattered along the platform with that glazed look people get when, against all odds, the sun finally breaks through the British cloudscape.

A couple appear on the platform. Not a very beautiful couple: he has a Lemmy from Motorhead moustache, wears horizontal stripes stretched across a Buddha belly, and seems to subscribe to the "if you don't wash your hair for long enough it starts to clean itself" myth. Her hair is pulled up lankly into one of those Essex girl ponytails that make women look as though the back of their skulls are pointed, and she wears a Tammy Wynette T-shirt under the top half of a shell suit. They have with them a large quantity of supermarket bags full of fizzy drinks, and a child. Lemmy walks ahead with a 2-litre placcy bottle of something sticky tucked into his armpit, she follows up with pushchair and several more gallons of brightly-coloured goo.

It being a hot day, Kiddie has been tucking in liberally to the drinks on offer. His T-shirt is dotted with smears of cherry and botulism-orange dye, and he jiggles and squirms in his chair. When they reach the benches, his squawks raise a few decibels as he strains to be released from his straps. Mother plonks down, surrounded by a mountain of bags, and undoes the straps. Father grunts something about getting some peace, waddles off to the sunny part of the platform with his fingers poking between tum and waistband, and starts picking the paint off the fence. Kiddie, free at last, races around, howling, and mother goes off into a fugue.

I follow suit. Consider the lilies of the field, or at least the burdock of the railway embankment. Wonder why lupins find it so easy to grow wild but refuse to do more than provide snail-food in my garden. Stretch to see if the macarena people, who have moved on to salsa now, would be worth a visit. Wonder which 14-year-old I should take to Florida this summer, and what we would talk about in the queues at theme parks.

There's a shriek further down the platform, followed by concerted bawling. Everyone turns to look, and sees that Kiddie is lying on the ground behind the bench where mother has been sitting, having obviously climbed onto it and somersaulted over the back. Mum is getting up, going "ooh, baby" and all those other maternal articulations.

She's too late. Lemmy is thundering up the platform, purple in the face; the force of his footsteps must be setting off earthquake warnings; I can feel the ground tremble beneath my feet as he approaches. He is shouting: "Get off him! Get away from him!" Kiddie's face is such a picture of pigeon muck and snot I'm surprised the Lottery commissioners haven't applied to buy him for the Tate. He rubs his eyes with the back of his hand, which, being grazed, adds blood to the whole sorry mess.

Lemmy reaches Kiddie, snatches him from the ground like a rugby football. The force knocks the wind out of the child for a couple of seconds, then he shrieks with redoubled force. Mum walks toward them, arms outstretched like an extra in a George Romero movie planning to bite a big chunk from someone's neck. He backs off.

"Don't you come any nearer, Pauline!" he shouts. Passengers are coming through from the other platform to see what's happening. "You've really gone and done it this time!" "I..." says Pauline. "No! No! You were supposed to be watching him!" "He..." says Pauline. Kiddie is squealing with something that sounds like pain as his father squeezes him about the head. "That's what you're meant to do! Watch him! What sort of parent are you?" He lets forth a string of swearwords worthy of Liam Gallagher, only with none of the lusty Mancunian charm. He hasn't actually checked to see which bits of the child are hurt.

Then Pauline finally finds her tongue. "Well, where was you?" she says. "If you think it's so important to watch him, how come you weren't doing it?" He pauses for a moment, then a roar comes from his hairy mouth. "Because it's your bloody job!" he shouts. "Don't try and come excuses with me. You've made a big mistake this time, Pauline. A biiig mistake." Thank God we have men; the role they play in explaining female dereliction of parental responsibility while they are off doing important things is essential to the survival of humankind.

Kiddie has extracted his arms from the paternal stranglehold. The first thing he does with them is stretch them toward Pauline. "Muuummeee!" he wails. Lemmy glares at him. "You don't want her. Look what she's done to you." Kiddie wriggles in his grasp and strains to get to his mum. Lemmy has one more try. "Just you wait till we get home," he says. "I could kill you for what you've done." Then he roughly hands the child over, where it wraps its arms round her neck and wipes snot on her collar.

The train pulls in. Lemmy picks up his bottle, hits the open door button and strides on board. Pauline, child hanging from her front like a little chimpanzee, collects pushchair, handbag and supermarket carriers, and goes to stand by her man.