INTERIORS / Coats of many colours: Choosing wallpaper and carpets doesn't faze Louise Cotier; she just paints the pattern she wants directly on to any surface. Dinah Hall calls on a creative spirit

THRESHOLD rituals have become the latest addition to fashionable homes. At the most basic level you have the house owner who opens the door and looks straight down at your feet to assess what threat your shoes pose to the parquet flooring, while in more sophisticated households you are greeted by a tactful rack of embroidered slippers in assorted sizes. But Louise Cotier has a much more arresting opening gambit. She proffers a lurid plastic pump-action water pistol and instructs you to 'shoot him if he makes a nuisance of himself'. This seems a little extreme as the six-month-old baby she is holding in the other arm looks quite harmless, but then each to their own, and it's probably high time the tide turned against the Penelope Leach approach . . . Fortunately, before there is time to squeeze the trigger a manic dog hurtles up and tries to vault over your shoulders, so the anti-terrorist device suddenly fits in to place.

Billy is a decidedly undecorative dog, as well as a social liability. He is neither an appealing mongrel with attitude nor the latest jolie-laide pedigree. This, together with the fact that his mistress doesn't so much as glance at my filthy policeman's boots, eliminates prejudice number one: that people who live in large London houses within striking distance of Portobello Road are going to be just too rich and fashionable to be likeable.

Having fought off the canine assault, it is the house that then grabs you by the throat and shakes you. It is just wild - a mad vortex of colour and pattern against which the hyper-active antics of the dog seem quite tame.

There is certainly nothing tame about the way Louise Cotier has applied her paintbrush to the walls and floors, seemingly following no rules of pattern and colour combination but ending up with rooms that flow in to each other in a rich tapestry of effects.

This lack of inhibition has not gone down well with prospective nannies who in this area expect a certain decorum from their employers - nothing more adventurous than Osborne & Little, if you please. 'Let's face it, Mrs Cotier,' reprimanded a stern Norlander in starched uniform, 'I am not the nanny for you.' Perhaps she had glimpsed the sofa on which Louise had drawn naked portraits of herself and husband ('this is me as I would like to be,' Louise hastily explains of the wasp-waisted, pert-bosomed creation). And of course it does become difficult to tell children not to draw on the furniture and walls when Mummy does it all the time. Another interviewee whimpered to the agency that it just 'didn't feel like home'.

She was right, of course. It feels like Mexico, Morocco, Scandinavia - all mixed up with a dash of Brighton Pavilion and a pinch of Bloomsbury. Louise takes her visual references from a variety of sources, from Mexican embroideries to Swedish decorated furniture, and is not purist in approach or technique. Generally the paint comes straight from a tin - none of this fashionable messing around with pigments and limewash - and if looked at closely the work relies more on bravado than painstakingly correct detail. Surprisingly, Louise Cotier has never travelled to many of the countries that inspire her - she has never been to India or Mexico. 'But I've been to Southall for the sari curtains upstairs,' she says, adding ruefully, 'Still, everybody's doing that now, aren't they?'

Just looking at the work Louise has put in on the floors, walls and ceiling is enough to make the average person feel exhausted. What makes it worse is that many of these rooms are on their second time around and she shows no sign of stopping. 'I'm a bit bored with the yellow in the drawing-room,' she says threatingly. Her husband, photographer James Cotier, is used to these constant transformations, so he probably won't be too alarmed to hear that her plans for the pink-and-turquoise painted dressing-room - 'a bit near the edge, those colours' - which he may have thought was finished, involve the addition of some large purple swirly things.

In the early days, she says, he did interfere, to the extent of asking 'what tone I was going to use'. He was a bit worried when the pink first went on to the new kitchen/dining extension. 'It did look a bit like the inside of someone's stomach,' Louise admits, 'but as soon as the blue paint went on with it, it was fine.' In any case, she says cavalierly, 'You can always paint it over if you make a mistake.'

Louise Cotier is not unsympathetic to the tortured relationship most of us have with the paint pot (the hours spent agonising over the colour charts before deciding, with a mixture of relief and cowardly guilt, on a creatively named version of white), it is just that she herself is unaffected by it. Having left advertising to concentrate on her emerging skills as an interior decorator, she started painting small pieces of furniture after the birth of her first child. As her work before was very much of the minimal palette - the bare plaster walls and muslin curtains look - this was quite a radical departure. After a while she could no longer contain herself on chairs and cupboards and started breaking out on to walls and floors.

'People find it quite shocking; I suppose they still like Laura Ashley prints,' she muses, adding quickly - but too late - 'not that there's anything wrong with Laura Ashley prints. And I think that the house suits it, don't you? You couldn't necessarily do it to smaller proportioned rooms but here you can get away with grand colours.'

Architectural historians would probably beg to disagree. They might not think that the hacienda feeling in the kitchen/dining room was exactly in keeping with mid-Victorian grandeur, nor that the French chateau look in the drawing room was in harmony with the Tyrolean chairs encountered around the house. But the children like it - and so do the electrician and the man who came to repair the fridge. Funnily enough, it's often the people she expects to like it or to at least react in some way who come in to the house and utter not a word - a silence that speaks louder than the walls. 'I mean, I'd rather they came in and said 'Yeeuch',' says Louise. But then that is very English middle class - like sitting through a spectacular dinner without making any comment on the food because it's considered 'not polite'. Louise Cotier's decoration may well be just too much of a personal declaration for some people. Like the Ndebele women of South Africa with their painted mud huts, she has splashed her soul across the walls. Perhaps a Ndebele nanny is the answer?

(Photographs omitted)