Linda Barker could revolutionise your sitting-room with a few sheets of MDF, a pot of lilac paint and an old tree branch. The star of the TV series `Changing Rooms' invited Ann Treneman for a good nose around her own house in south London.

Linda Barker is not just any interior designer. She is a star of the hit BBC programme Changing Rooms and the author of almost a dozen books. She knows how to do amazing things with MDF and only needs a few bits of copper pipe to make a four-poster bed. She manages to make DIY look sexy and has a lot to teach a woman like myself who views putting up a shelf as a major engineering project. But I am not in the mood to learn as I stand on her doorstep in deepest SE23. I am in the mood to snoop.

I have always been a decor voyeur, but then I think most of us are. Witness those people who spend all their free time going round houses on the pretext that they may be buyers. In reality, of course, they are frantically clocking the paint effects and wondering if they too shouldn't try a dado this year. All readers of Hello! are decor voyeurs - the words are just wallpaper for the wallpaper, really - and so are each and every one of the six million or so viewers of Changing Rooms. The programme follows two sets of neighbours as they transform a room in each other's homes, each egged on by a designer.

"The British are very nosey people," says Linda Barker. "People love to be nosey and the programme lets them into people's houses."

I nod, but my mind is really on her kitchen. It is light, airy, sunny. "Is that rag-rolled?" I ask, looking at a wall that seems to be dappled. "Frescoed," she says, explaining about how you do four coats and it's no trouble, really. A hand-painted olive branch drifts across one wall. The only sign of her five-year-old daughter, Jessica, are some chocolate fingers set out on the bleached wood island that serves as a sort of giant chopping board. I nibble on one and then another.

"Did you do this yourself?" I ask in a small voice. "Hmm, yes, the whole house really."

At this point, I abandon all attempts at interviewing her about the book she has just written on Changing Rooms and ask for a tour. She complies and is obviously a bit of a pro at this. She and her husband moved to the large Victorian house in Forest Hill from a tiny flat in Battersea. It has five bedrooms, high ceilings and wide hallways. It came with the proviso that it needed modernisation. In the end, it needed a whole lot more than that - Linda spares me the details, it is clear that it was not a picnic - but now it is pretty ab-fab by any standard. I see bits of the Changing Rooms everywhere - a painted gingham wall in her daughter's bedroom, a hand-blocked blind in the playroom, the Italian calligraphy flowing over her bedroom walls, the fake four-poster in the spare room. The upstairs bathroom is graffiti'd in Latin and reads: "You look like someone who knows a good thing when you see it."

We stumble upon her husband in the study looking up alternative words for "junk" in the computer's thesaurus. Linda has just published yet another book, this one called Just Junk, and it has been such a hit that she is doing another one in a hurry. "But we can't use the word junk again," she explains.

I nod, though I don't really understand why this is not possible. But by this time I'm beginning to understand that I understand nothing about interior design and that there is a little more to it than a fresh coat of primrose white and a trip to Habitat for some hand-tied curtains.

But I have also figured out that Linda herself is a bit of a designaholic. After our interview she is heading off to Winchester to record another television programme, called Change That, in which she has four hours to transform a piece of furniture. She is an art school graduate who is now 36 and having too much fun. She doesn't like to stand still or look back, particularly. The thrill is in the doing.

She has just finished filming the new series of Changing Rooms that will be shown in January.

"I just love the fast turnaround of design. For me it's a bit of a dream, being given a room and being told to throw pounds 500 at it, design it, change it as much as you can. That is a joy."

She thrives on deadlines - three rooms in her own home only got done on time because they were going to be photographed for a magazine the next day - and diversity. "I mean, for this new series I did a Caribbean houseboat. That was fantastic. People let us into their rooms and allow us to do whatever!"

Not quite. What actually happens on Changing Rooms is that the neighbours tell a designer like Linda what they think the people who actually live there would like. The designer then goes away and comes up with a plan that can be achieved in two days with a budget of pounds 500. This requires a lot of people-skills and elbow grease and makes for compulsive viewing.

Linda insists that there are rarely any real problems, though, with prodding, she does admit to the occasional tiff. There was the one time when the couple hated the room and said so, on camera. Then there was a bit of a controversy about a branch she'd hung on the ceiling to dangle lights through. "I needed something dramatic up there. I'd spent all my money already so I did that," she said. In the end, she says, they came round.

Then there is the delicate matter of the couple she is working with. "They can get worried and want you to adapt colours, say. I can think of one time that I had picked a blue. It was very tasteful and we were painting it below a dado. We had done this fake tongue-and-groove wall panelling that we'd spent ages on. The woman was very anxious about the colour and got a little bit sulky." So sulky, in fact, that she put down her paintbrush and went into a huddle with her husband, bad-mouthing the colour. Of course, Linda knew that it would be fine (which it was) as soon as the fabric with the red was added to the room.

The worst is when even the crew starts to doubt her vision. Linda herself never does - except for the time she decided the shade of lilac really was too much like a bar of soap - and sticks to her original plan like stucco.

"By the time I have come round to decorating it would take a bit of an earthquake, really, or a major tantrum to shake me from my vision. So, yeah, I am very confident. Thank God, or I would be a quivering wreck."

It is at this moment that I realise Changing Rooms would make me a quivering wreck. The book shows 16 room make-overs and it is worrying that I feel more comfortable with some of the "before" pictures. I have visions of my nice (but sad) primrose kitchen being turned into something exciting, hot and Mexican. This is a tough game, I realise, though I can't help but take a final snoop at her lovely green hall with matt black radiators as I leave.

Linda Barker's `Changing Rooms' is published by BBC Books at pounds 16.99.