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My son's mother has had three kids by three different tradesmen. She had mine first, when I was the dustman; the second was fathered soon after by the mobile greengrocer, then she had a third by the milkman. Lena is agoraphobic, and has had to take what comes along. Fortunately for everyone concerned the milkman fell in love with her, and moved in. Later he gave up the milk round and became a flat roofer.

We've all kept in touch except the mobile greengrocer. Sadly he didn't want to know his son, a lovely little boy called Jack (after Jack Daniels). When Jack asked where his dad was, we frankly told him he ain't got one. He was downcast at first, but took heart when the ex-milkman and I promised to be his best friends.

My son Tim, who is nine, lives with his Mum during the week and comes to me at weekends. This means, among other things, that Tim moves between two very different social classes.

Lena is lower working-class verging on underclass. At her house, it's all blood pressure tablets, swearing, fatty foods, sad pets, and a cheap brand of cigarette called Royals.

When Tim comes to us for the weekend, however, he moves up a rung: for we in our house are lower middle class, the old NCO class, the middle classes' bulwark between themselves and their worst nightmare. In our house we have carpets, lined curtains, a fruit bowl, and a framed photograph of Sir Winston Churchill hanging in the hall. And if Tim looks in the bin, he sees that our potato peelings are much thinner than his Mum's are.

In spite of Mrs Thatcher enriching us, and Tony Blair enlightening us, we are still stuck in the lower middle class, and the middle middle class is still as far out of reach as it ever was. Not that anybody here is seriously thinking of joining, mind.

Sometimes of a Sunday morning, I take Tim to a small and permanently crowded local trattoria called Pravda, which is a stronghold of the local middle middle class. I take him there as part of his education. We sit at one of the tables if we can get one, and we sip and watch and eavesdrop, unjudgementally, like spies. We don't comment. We don't know enough about what we are looking at to comment sensibly. We just observe. Tim was frightened when we first went there, but now I think he actually enjoys it.

Last Sunday Pravda was heaving as usual. Luckily we managed to get a table, right next to the jazz duo, who were setting up their equipment. "How's the wife, Les?" said someone to the saxophonist as he screwed in his mouthpiece.

"A bit more with it, thanks," he said, giving his instrument an experimental parp. "They're juggling with her painkillers at the moment."

There was a fat middle-aged man squeezed on to our table. Finding me and the boy uncommunicative, he had turned to the table next door and was reporting on his recent audience with the Dalai Lama. He had made the pilgrimage with a group of other seekers after enlightenment, apparently. The design of his glasses suggested he was a man of considerable intellect.

The main thrust of the Dalai Lama's message to the group was that if any of them had sex in the afternoon they'd go to hell.

"When the Dalai Lama finished speaking, this French guy totally freaked," reported the man with the glasses. "He went nuts. He shouted at the Dalai Lama, `Do you mean to tell me that I've come over 10,000 miles to be told I'll go to hell if I have sex in the afternoon?'"

And the Dalai Lama had told him yes he had.

The place was absolutely packed - yet people desperate for Pravda's expensive food were still trying to push their way in, to the accompaniment of the up-tempo beat of the two-piece jazz band.

In the midst of the crowd was a very old man, possibly a vagrant. Tim pointed him out. He was capering about and playing the spoons. He seemed lost in the music - he had a peculiar ecstatic look on his face. And as the boy watched, he was shoved roughly aside so that he lost his balance and fell on the floor.

Nobody helped him up.