The tree is up - or it was. But Jonathan adjusts the base one last time and the whole thing crashes down ("Christ-Julie-quick-bloodyhell- Julie!"). I catch it calmly, return it to the vertical position.

"Why did you let go?"

"You told me to."

"Is that straight?"

"I can't tell this close up."

"Well, get back then!"

"If I get back, I'll let go." Kids in fuzzy dressing-gowns and slipper socks swarm around our feet.

"Back, maggots, back!" Their father shoves the small bodies across the varnished floor.

"Don't kick my children."

"I'm not kicking, I'm moving them with my feet."

"When can we start putting things on?" moans Jacob, punching the sofa (and then Chloe) with his fist.

"OK, be patient," I try to stall them. "We've got a bit of a problem here."

It's the problem we have every year. Isn't Christmas all about repetition? The tree stump always fits in the red metal tripod but won't ground itself.

"We could just decorate it down there and then put it up," suggests Jacob, who wants - at any cost - to be the one to hang the striped zebras on the tree (having hoarded them up under a cushion which he's now guarding).

Playing for time, I get out The Snow Scene. Some of the pieces - eight reindeer, eight gnomes, each with a different instrument, plaster houses, robins, a compact mirror for a lake, rosy-cheeked Father Christmas on a sledge - have been with me all my life. Even the smell of the felt and sparkle and old plastic brings the Christmases flooding back.

A long time ago, we lived in a house in the centre of Nottingham and the church bells at the end of our road weren't real ones but a record, and at Christmas they put carols on. Sometimes the record got stuck - "Oh come all ye - oh come all ye - oh come all ..." This would go on for some time. My mother had recently remarried, which meant our family was really two families joined together. She conscientiously poured all her energy into a Christmas Day that would unite all sides.

Sometimes this meant Christmas lunch for up to 20 people - most of them elderly - and it had to be over by 3 o'clock so "people" could "catch" the Queen. Squashed up along our long refectory table were grannies and great aunts and aunts, sisters, stepbrothers and - when he was allowed - our grandfather, who never came without Jesus in tow.

Our step-great aunt, Glenda, had taught at the Derbyshire school where DH Lawrence's lover had worked. Glenda's sister, Mary, our step-granny, had worked at Boots as a young girl and married a man who bossed her. In widowhood she herself became fierce and bossy ("Making up for lost time," her sister called it). She liked to fall asleep with a sherry glass - "Sherry? Ooh, what a treat, I don't know if I should" - in her large, arthritic hand.

"Please look after the grannies," beseeched our mother. Our real Granny - Hungarian, plump and brown as a baked apple, adorable - wore fur-lined, zip-fronted boots and liked to talk about the price of brussels. Our stepfather's sister, Auntie Jean, out of the local mental hospital for the day, was extremely fat and wore a skirt with red London buses on it, made from an old kitchen curtain. Jean could sit for hours watching cartoons on TV and had an adoring crush on our mother.

A typical conversation: "Is that blue you're wearing, Maritza? I do love it."

"Do you, Jean?" - our mother always addressed her with great respect - "Well, thank you. I got it at Debenham's actually, in the sale."

"I love it, you look like a princess - you are attractive, you know."

"Jean," (little laugh) "that's very kind."

But a few minutes later, our mother would offer Jean the bread sauce and she would jab a finger into the air and say aggressively, "Do I know you? Have we met before?"

"It's me, Jean, it's Maritza."

"Oh. I thought it was you. Is that blue you're wearing?"

We children didn't like Jean because she was ugly. She had great purply, crackly burns on her legs where she'd pulled her chair up too close to the gas fire, and her grey hair was specked with dandruff, and she smelled of pee. Our mother always went out of her way to give her glamorous Christmas presents. Once she gave her some Estee Lauder perfume and Jean wept with surprise and pleasure.

Sometimes Grandfather (surrounded at Christmas, he thought, by potential converts) tried to tell Jean about Jesus. "Have you heard the Good News about Jesus?"

"Jesus who? Do I know him? Is he here?"

"Jesus Christ! He's alive and He's here!"

"Oh good, we could do with some more men - I don't know whose this party is, but have you noticed it's all women?"

Well, 10 years later that stepfather was no longer in our lives and Auntie Glenda got pneumonia and died and - years later, apparently - so did our step-granny. I don't know what happened to Jean. Sometimes, when a family that was never really yours disperses, you don't know what to think - all those Christmases.

The Snow Scene's still here. We lay it out on a roll of cotton wool, with inverted tea cups as hills. Auntie Jean always remarked on the Angel with her dolly lashes and little round "O" of a mouth. "That Angel's nearly as old as me," I say when Raphael kisses her. Jonathan snorts.

The tree - now successfully balanced and threaded with fairy lights - stares down soberly at us, about to be draped in sentiment.