We knew it was serious when the assistant bought us a drink

"CAN I help you?" means different things in different shops. In some it can be roughly translated as "I think you'll find these clothes are far too expensive for you, and your presence here is an unwelcome blot on a minimalist landscape", while in others it simply means that the staff have been on an American-style training course and will have their arms and legs pulled off if they can not approximate some semblance of helpful intent.

On the first floor of Liberty, however, it is a question that can be taken at face value as you struggle with the concept of a pair of Yohji Yamamoto trousers with a giant plaited penis hanging over the waistband. And, yes, I felt I did need some help with the Martin Margiela jacket. Really, all I wanted to know was whether you put your arms in the sleeves or in the hole behind them, but what I got was a kind of philosophical treatise.

This jacket was all about the "deconstructed silhouette" and was part of a collection which celebrated flatness. "See" said the assistant, holding up a transparent top on a. hanger "it is just like a carrier bag." `This was absolutely true, but what she and Martin had not anticipated was that once I was inside it, it would look like a carrier bag containing the weekend shop.

I would love to have bought something from this walking thesis, particularly as she gave no hint of having spotted the ingrained Cadbury's Boost down the front of my Marks & Spencer's top. But this shopping expedition was in celebration of the fact that the children are now old enough for my clothes not to have to double as face cloths (the Boost was mine). And I was just not ready to go from wearing an expression of my children's tea to wearing an expression of a designer's tortured ego.

So, to Donna Karan, armed with my sister, who has a great eye and as a lifelong Hennes shopper would, I reasoned, act as a buffer between me and the sales assistant's commission. Would she hell. "I think you have to have the top," she opined. A sleeveless top for pounds 125, that was, I discovered when I got home, "100 per cent polyester". What I really needed was the jacket and trousers but because my sister is older and knows better, I took the lot - plus the scarf which the assitant said I had to have, and who am I - Marks & Spencer woman - to disagree?

I can't tell you how much it came to, In case my husband's reading this, but we realised it was serious when the assistant escorted us down to the bar for a drink on the house. "I don't think any capuccino will ever taste as good as that free Donna Karan one," sighed my sister dreamily the next day over her Nescafe.

I had to remind her that mine didn't taste quite so good as it had cost, um, several hundred pounds. Anyway, I gave her the carrier bag and wrappings to take back home with her - in Norwich, she says, people would pay just to sniff DKNY tissue paper.

The new outfit does not fit in with my son's plans to downsize me. He has hidden my earrings and will only allow me to watch his school football matches if I will wear a shell suit and promise not to pick him up in the Espace. But I feel I have a job to do there on the sidelines - a sort of one-woman UN peace mission.

"Calm down, boys" I chided the fathers last week as they roared instructions to the players and questioned the gender of the referee "it's only a game."

A game? they bellowed incredulously. "This is football," said one, passionately clenching his fist against his heart, "it's in the blood." It was a moment of pure epiphany: shopping for expensive clothes is just like football - it's in the blood. I think my husband will relate to that.