An investment, after a fashion

Women are well-versed in the art of justifying what their partners would consider unnecessary purchases. More often than not the self-deluded logic runs along the lines of, "It was reduced from £200 to £100. So really I saved £100". But what about this as the ultimate justification for splashing out half a month's salary on the designer dress you have been coveting for the past two weeks: it is an investment.

This is not as far-fetched as it first sounds. There is a thriving market for second-hand designer clothes and accessories. The trick is knowing what and who is collectible.

The sought-after designers going under the hammer at the moment are Yves Saint Laurent, Cristobal Balenciaga, early Christian Dior and Chanel, Madeline Vionnet, Paul Pioret, Elsa Schiaparelli, and Mariano Fortuny. Homegrown designers also get a look in, with Vivienne Westwood, Ossie Clarke, early Mary Quant and Biba all proving collectible.

This is a recent phenomenon. Ten 10 years ago all of the big French and international fashion houses would have ranked in any list of most desirable labels, there were few, if any, British designers. Kerry Taylor, a fashion specialist at the auction house, Sotheby's, puts this down to the fashion world and museums finally waking up to their importance.

The items that never fail to attract buyers include seminal pieces by great designers at their peak. Dior in 1948, for example, always does well at auction but Dior in 1957 or 1962 does not. Chanel suits also have a faithful following, as do Thirties-inspired Ossie Clark dresses, Emilio Pucci psychedelic wear and Andrè Courrèges futuristic items.

Accessories such as Hermès handbags are also popular. In the last sale on 19 May, a late 20th-century Hèrmes black, lizard-effect, Kelly bag fetched £6,000, and a rare Gucci brown combined handbag and escritoire, again late 20th century, went for £1,800.

But if you do not have a seminal Chanel languishing at the back of your wardrobe, the designers to look out for now, and to wear now, are Alexander McQueen, John Galliano and Azzedine Alaïa. Ms Taylor says: "All understand construction; they all understand how to flatter the female form; they all have the imagination, daring and skill to stand apart from the rest. Their clothes can be radical but also wearable."And this, it seems, gives them lasting appeal.

Other designers who have proved their worth include Jean-Paul Gaultier. His "Femme" chartreuse taffeta evening ensemble, from 1990, was recently sold at auction to a private collector for £2,350. And an Ossie Clark dress and jacket auctioned at Sotheby's raised £3,450. It is worth while keeping your eye on the designers going under the hammer to act as your barometer for which labels are selling well and which are not.

Shoes and handbags regularly go up for auction, but they have to be in excellent condition and by major brand names or designers such as Gucci or Hermès. Louis Vuitton, too, is collectible. In particular, the limited edition Graffiti bag has proved very desirable, and it retailed at £250. Shoes will attract attention if they are funky or "works of art". Some people go so far as to display Vivienne Westwood super-elevated platforms on their mantelpieces, Ms Taylor says.

The decision to sell your prized designer dress or handbag is just the start. The next step is evaluation. Approach a fashion expert at an auction house and they should provide you with a preliminary auction estimate. If you cannot make it in person, then you can post photos of the item you want to sell along with an auction estimate request form (which you will get from the auction house's website). Responses can take some time.

If the auction house decides your property is appropriate for sale you need to agree a reserve price. This is the confidential minimum selling price, the "floor price" below which no bid will be accepted. If bidding on your item fails to reach the reserve, the piece will not be sold. If successful, you will be liable to pay a selling commission. This is deducted, along with agreed expenses, from the hammer price.

A further expense comes in the cost of the packing, shipping and insurance charges when you send the items to the auction house. You are responsible for all of this.

So who are the likely buyers going to be? In the first place, museums and specialist collectors who collect to display but would never wear. Then there are fashion designers seeking inspiration and the private individuals who are buying to wear the items. Common sense should dictate that no one is going to want to buy a threadbare or faded garment, or a damaged accessory, so you need to keep what you intend to sell in good condition.

But Ms Taylor says it is still possible to get a decent amount of wear and enjoyment from your purchase before it is sold. "Most of the pieces I sell are from 'ordinary' women, who have worn the pieces before sale," she says.

Sotheby's holds its annual Passion for Fashion auction in November or December, offering jewellery, designer clothes and accessories This sale was started in 1998, and has grown to be a milestone for fashion connoisseurs and aficionados, attracting museums, private collectors, designer devotees, and trade dealers.

The sale includes vintage and antique clothing, alongside couture by designers such as Chanel, Balenciaga and Givenchy. Street fashions by the likes of Biba and Vivienne Westwood, and classic fashion magazines, illustrations and sketches, are also auctioned. The jewellery offered includes rare and period pieces, as well as work by leading makers, such as Cartier, Tiffany, Bulgari and Van Cleef and Arpels. But it is not all about couture. In December 2000, the Passion for Fashion auction included a collection of Punk fashion from one person. The owner started the collection as a teenager in 1976, when he bought Spiderman bondage boots at the legendary Seditionaries boutique on the Kings Road in London, run by Vivienne Westwood and Malcolm McLaren.

He added to the collection with items such as a white cheesecloth shirt displaying an X-rated version of Snow White and the Seven Dwarfs, and a selection of T-shirts including Sex Pistols Anarchy and Tits designs from Seditionaries and its successor, World's End. The collection sold for £8,460.

The next "Passion for Fashion" will be on 27 November. For further information, call 020 7293 5555