Look where my big mouth has got me now

Last Thursday at 9.30pm, I did something even I couldn't believe I'd pull off. I walked down a catwalk in Milan, watched by 850 people, modelling three dresses in a top fashion show. I know you're incredulous. From rambling to runway - is she nuts? How does it feel to stand naked, backstage, while two Italian seamstresses pull clothes on and off you at lightning speed? What about all those gorgeous professional models? What about my cellulite? My glasses?

The story started two years ago, but here's the latest installment. The phone rang on my birthday, 27 December. I'd eaten so much lunch I was lying on my bed, bloated. It was good and bad news. My friend Antonio d'Amico had called from Milan to wish me happy birthday, but also to remind me that, in an unguarded moment last summer, I had agreed to model his first solo collection. Panic set in. How could this shapeless white body swan down a catwalk and look elegant in just over 14 days time? A new regime started - but not until I'd celebrated New Year, of course. Antonio had told me to "be myself", after all.

I had met Antonio d'Amico at Elton John's house the summer before last, shortly after Gianni Versace's murder. Antonio, his lover for 14 years, was simply one of the most dignified people in grief I had ever met. There was no doubting the depth of his loss, and so our friendship started at the lowest moment in his life. But he was an inspirational person, and certainly helped me to deal with my mother's death this summer.

Elton had known Gianni and Antonio extremely well, and was very supportive when Antonio finally decided to launch his own collection. How could I churlishly refuse to model? He told me his clothes would be modern and simple, and that he would use a combination of real people and models. After all, he reasoned, customers are not super-thin. They are real shapes and sizes.

How could I, at 52, not look a complete disaster? For years I've whinged on (like most women) about stick-thin models dominating our images of fashion. Now I had a chance to put the JSP point of view into action. So I didn't diet, but tried to remove festive excess from my torso. I was a size 10 at the age of 18, but for the last 10 years I have been either a big 12 or a 14. And nothing would change that.

Luckily, I had a book to write and the deadline was upon me. So, at my cottage in Yorkshire I adopted a lentils, brown rice and vegetable regime. No drinking for three days, then a one-night binge in London and then back to three days of abstinence. Lots of apple juice and water. Loads of trips to the loo.

The night before take-off I lapsed, but I had still lost 5lb on the JSP diet. Good. But I had a cold. Bad. Nothing would remove the bags under my eyes. I would have to smile a lot and incorporate them into laughter lines. Grinning also disguised my baggy chin. I practised the walk - a lot - in my friends' kitchens. All the gay men could do it perfectly, thrusting their hips forward and their shoulders about one foot back. Not one woman could.

I arrived in Milan, to find a huge bunch of flowers in my hotel room, and spent two hours being fitted for my clothes. Basically, you take off all your underwear and bits of fabric are draped on you, cut on you, pinned on you. Nudity isn't a problem. The seamstresses have seen it all before, the male models are all gay (spending their time eyeing each other's biceps) and the female models ignore you, because you are fatter than them and thus simply don't exist in glamour world.

Back at the hotel, I stuck on a blue "revitalising" face-pack and fell asleep, awoke late for drinks with David Furnish, Elton John's partner, who was also modelling, and shoe designer Patrick Cox. We had a great dinner - I ate risotto and liver and fried potatoes, plus vanilla ice- cream. Then I had to go back to Antonio's at 11pm for more fittings. Now all the clothes were too tight. There was a lot of tutting.

Tuesday morning. I ate a croissant for breakfast. I will not be a slave to fashion. Go to the Nuovo Piccolo Teatro (where the show will be held), as requested, at 11am. Nothing happens. They are still building the set - it has a departure lounge on either side and a silver runway with lights up the side. I'm bored out of my brain. How do these models do it? They just smoke, drink water and witter endlessly on their mobile phones. I get a newspaper out and they look at me as if I'm mad.

The other people turn out to be dancers (great figures), body builders (great bodies), an antique dealer (also does weight-lifting), some gorgeous young Italian men from very good families with fantastic faces, and one or two extremely stylish older women. David and I have named ourselves as the Plucky Brits. We decide to drink champagne before the show, especially as poor David is to be the first one down the catwalk.

Finally, at 4pm, we have a rehearsal. People shout your name out and you stand in line backstage - just like school. On my first entrance, I trip on the step up to the stage and rip a chunk out of my arm. It's covered in blood. At least now I'll get some sympathy.

Back at the hotel I order bandages and throat lozenges. I don't think a hacking cough is a great accessory. Rumours are sweeping Milan. Will the theatre be full? (It was.) Will Donatella Versace be gracious enough to go? (She wasn't.) Why can't people who worked together for 10 years be generous? But then I remember. I was a fashion writer for four years once. How could I forget what the fashion business is really like? A world of giant egos and massive jealousies. Panicking, I shave my armpits yet again, slick on another "rejuvenating" face-pack and eat a plate of smoked salmon and two bread rolls. That feels much better. I wash my hair, and the red dye leaves the marble shower and luxurious white towels looking as if a serial killer has visited Room 364.

Back at the theatre at 7pm, I queue to have my hair and make-up done. The room is baking. I take my sweater off and walk round in a flesh- coloured bra - no one cares. My hair is turned into a red pagoda. It takes 30 minutes of ironing it straight and then a whole can of lacquer. It looks great, feels like steel. Make-up - I choose the old man making up the snottiest real model. He does a wonderful job of making me look brown and natural. It takes another 20 minutes to make me look like I'm wearing no make-up. I say thank you. No one else has thanked him, it seems. I put the first outfit on and wait and wait.

We start 30 minutes late. All the Brits cheer when I come out. The Italian press are confused. Who am I? Am I famous? It all passes in an instant. I don't fall over, do a lot of grinning, and bring Antonio on at the end for applause. The press ask him, who is Janet? He kindly says, "My favourite model". They ask me: "Are you a model in England?" I just crack up."No, I have a real job!"

The show got great reviews, and it seems the clothes were thought to be stylish and confident. So I'm pleased for Antonio. But would I do it again? You've got to be joking.

On Wednesday, there were large photos of me in the Daily Mail, the Mirror and the Express. Cliches galore, of course, from "Pret-a-Porter" to "TV presenter gets her teeth into fashion", but I'm not complaining. After the nasty press I've had based on big teeth and a bigger mouth, this coverage was positively friendly.