Why on earth did I buy it?

Lisa Armstrong reports on a charitable sale of orange suits and other sartorial disasters.

With the catwalk shows in Paris just over and those in New York about to start, it is perhaps a good time to consider those fashion moments we would prefer to forget. The most cursory flick through Hello! confirms that everyone makes mistakes in the clothing department. While this is comforting, it begs the question why, no matter how well acquainted we are with our physical shortcomings, do we still get seduced by horrors?

The classic time for committing fashion suicide is during sales. You see some Thierry Mugler PVC chaps on the rail, reduced by several thousand - suddenly they seem a terrific saving and the missing link in your wardrobe. So what if you always wear tailored suits? You'd been thinking about updating your image anyway.

Sale transgressions are perhaps the easiest to understand. Being keyed up to spend and not finding anything that fits the bill can cloud the judgement of the most wised-up ''fashion expert''. The galling thing is that you usually know your common sense has fallen by the wayside as you write the cheque - but still you sign your name. Once a mistake gets home the problems proliferate as it clutters up the wardrobe, obliterating the things that do work.

The solution is to avoid all ''bargain'' areas unless you have something specific in mind (a navy blue pleated skirt, say) and can keep from persuading yourself that a fuchsia pencil skirt is almost the same thing.

Less easily controlled are the impulse buys made when you are at a low ebb. This is when you forget that however intrinsically beautiful a tulle crini is, if it magnifies your thighs, it is not a wise buy. Bobby Hillson, head of MA Fashion at Central St Martin's, wears her favourite outfit when shopping: ''If what I try on doesn't look better, I don't buy it.''

What makes fashion failures so humiliating is that they lay bare our capacity for self-delusion. It may be edifying to look at other suckers and wonder how they could have bought that - but it is not always other people who invest in outfits for the body or social engagements they wish they had. A colleague has dozens of clothes that would look fabulous in night clubs: ''only I go to night clubs twice a year. It's all very well my alter ego taking over in the shop, but I've nothing to wear to the office.''

Another plays so safe that she ends up with rows of identical black trousers and shoes. As for me, I still can't believe I wore swirly, fluorescent leggings. They went with nothing in my wardrobe - or my life; I can only assume that seeing them on Christy Turlington was a prime motive for that ''investment''.

Being carried along on the crest of a ''fashion breakthrough'' or allowing yourself to be lured by sohisticated imagery is asking for an unco-ordinated wardrobe. Following some trends is fine; the important thing is to know when their life is up. Hoods were a textbook example of obsolete-almost- as-soon-as-it-hit-the-shops fashion. Unfortunately, some people had paid a fortune for theirs and were determined to get their money's worth. Other directives should be avoided altogether; it really is better to be ''out of fashion'' than to wear miniskirts if you loathe your legs.

Once the worst has happened the best thing to do is admit it as soon as possible. ''When I worked at Vogue in the Seventies we were supposed to chuck out our clothes at the end of every season,'' says Caroline Baker, now fashion editor of Good Housekeeping. ''At the time I thought it a bit extreme, but maybe they had a point. If you never part with anything in the hope of making all these disasters somehow gel, you'll never work out a cohesive look.''

The most undermining mistakes are those that cannot immediately be rationalised - that wonderful jacket which for some reason never gets worn. The truth is that even if you got round to having it altered (extensively) and dyed, it would probably never feel right because it isn't the shape or fabric you feel comfortable in. It's probably worth forcing yourself before you leave the changing room to make a mental list of at least three occasions when you could wear a new outfit.

''My worst buys happen when I deviate from my normal style,'' says Bobby Hillson. ''That's when I decide my image needs changing so I'll buy clothes I don't really identify with.''

Caroline Baker adds: ''Think about clothing as architecture for the body. That way, before you begin to fret about whether it's ''good'' or ''bad'' taste, if it doesn't flatter your best features and disguise the bad points, it's a non-starter''.

No one entirely stops making clothing mistakes - after all, the joy of shopping is that it is an exercise in supreme optimism. But at least they can be put to better use. On 2 November, Fashion Acts is holding a sale to raise money for Aids research. Designers and celebrities as diverse as Kim Wilde (Jean Paul Gaultier trouser suit), Julie Christie (Comme des Garcons shirt) Ossie Clark (scarlet boots), Emma Thompson (orange silk trouser suit) and Elizabeth Taylor (Dallas cowboy jacket) have donated mistakes they wished they'd left in the shop - proof that everyone really does makes them.

OSSIE CLARK swept through the twin worlds of fashion and music in the Sixties and Seventies on a wave of genius and good times. Pals with such luminaries as David Hockney, David Bailey, Bette Davis, Mick and Bianca Jagger, he was also the most gifted creative force in British fashion.

The only dark cloud on his horizon was his refusal to apply himself to some of the basic tenets of good business practices. By 1982 he had given a lot of dresses away and been declared bankrupt. ''I was like a lamb to slaughter,'' he confesses.

Nowadays he designs for friends, who pay his telephone bill or buy him a washing machine in return. A cadaverous figure, he can be spotted regularly on the Portobello Road, picking his way through the market stalls.

''I don't often make mistakes with my clothes. I arrived at my style - English eccentric - some years ago and it doesn't really change. I buy all my stuff second-hand. I'm a freak about good quality. This poacher's jacket is fabulous tweed - you couldn't buy it new. The jodhpurs are pure cotton and lined; Ralph Lauren would probably charge £ 350 for them.

''The boots are another story. Strictly speaking they're not a mistake - I mean, I still like them but they've never fitted me. I bought them in Flip on Melrose in West Hollywood in 1983. The shop was owned by Alice Pollock, my old partner. When she saw me coming into the shop she said, 'Oh God, not you again, Ossie, I'm not getting involved with you again.'

''I said, 'Calm down, dear. I only want to buy something from your shop,' to which she replied, 'Take whatever you want.'

''So I took everything red. These boots are actually women's - I got the biggest size but it was still too small. Still, they're infinitely preferable to those trainers everyone wears today. I can understand being rebellious, but those are so sensible, and so ugly. We are breeding a nation of flat-foots.''

Caroline Baker, fashion editor of ''Good Housekeeping'', is donating an Emporio Armani raincoat, on sale for £ 50.

A veteran stylist on such landmark titles as Nova and Vogue, Caroline Baker has always been personally involved in fashion. Where other editors content themselves with creating revolutions on their pages, she has also regularly transformed her wardrobe: one year army surplus, another Donna Karan.

''I bought this three years ago because I love maxis - I've always thought they were romantic. But the reality of living in London and having to clamber up to the top deck of buses in them is another story. They always get wrapped around your legs or trapped under your feet. I'm not prepared to do an Isadora Duncan with my coat for the sake of looking good.

''Nowadays I try to be quite organised with my shopping. Every season I work out a couple of must-haves. This time it's a little pleated skirt and something tartan. But inevitably I deviate. I know you're supposed to shop around really throroughly before you buy. But I panic in case the shop runs out before I have a chance to come back. I'm terribly impulsive.

''My style has changed depending on each magazine I have worked on. When I was on Nova it was all combat gear. Mirabella was quite high profile, so I learnt to love suits. At Good Housekeeping I've come into contact with the readers as never before. It's my mission in life to get older women in this country wearing shorter skirts. I know designers are doing long, but they're just not practical.

The greatest mistake older British women make is to worry about looking like mutton dressed up as lamb. It's a ridiculous phrase - whoever invented it? I'm nearly 50 and while I hope I don't make a fool of myself, I still have great fun with fashion.

The Fashion Acts Great Mistakes, Dance Works, 16 Balderton Street W1; 10am-6pm. Minimum donation £ 1.