You can sit on a small fortune with old jeans.
A well-worn pair of Levi's from the Fifties or Sixties can change hands for £500 while makes such as Wrangler and Lee fetch £200 or more.
'You cannot go wrong with a great pair of old jeans - it's like investing in good property,' says Michael Morales, 31, manager of the vintage clothes shop One of a Kind in Portobello Road, west London. He says: 'Modern denims are a great cut and quality, but there is a better finish to vintage jeans. They were more a labour of love, with hand stitching rather than mass production.'
Levi provides the most collectable denim, with the highest-value pairs produced in the Fifties and Sixties and dated with the help of a red tab logo stitched into them. Earlier pairs do not have the same sought-after cut.
A 'LEVI'S' logo - jeans known in the trade as 'Capital Es' - was stitched on both sides in a red tab fitted to jeans in the Fifties.
In 1971 the logo lost the capitals and was rebranded 'Levi's'. It is the earlier 501 cuts that can fetch £500. Even ripped examples can fetch £300 or more.
Classic cuts from manufacturers such as Wrangler and Lee are also collectable, as are brands including Chipie, Chevignon and Farmer. Prices start from £200.
Designer makes such as John Paul Gaultier, Japanese label Evisu and the Signature brand of Gianni Versace are all renowned for their quality as well as cut and can sell for more.
Key to the appeal is the look of vintage jeans. No amount of stone washing and sand blasting will substitute for decades of natural ageing and this means wearers are putting on a unique pair of jeans.
Michael says: 'Jeans are to be worn. You just have to treat an old pair with care to avoid rips that may harm value.
'Being aged means they are already in true shape. But you should avoid the washing machine at all costs. If the jeans get dirty then hand them over to your local dry cleaner.'
The more colour the denim has retained, the more valuable it is while any rips and tears can slash prices in half.
The record price paid for a pair of jeans is $46,532 --more than £29,000 - paid in 2001 for a pair of Levi's that were made in the 1880s.
The history of cotton denim for clothing stretches back to the 17th Century. It wasn't until 1873 when Levi's patented riveted denims for Nevada miners that jeans were born.
Originally, they were made from harsh tenting material that Bavarian-immigrant Levi Strauss had been unable to sell. He then discovered French cotton 'serge de Nimes' - which became known as 'denim'.
But it wasn't until the Thirties that jeans caught the imagination of working men, who saw them being worn by cowboys in Western films.
Jeans were not embraced as fashion statements until the rebellious youth of the Fifties turned their back on conservative dress. Film stars of the era such as James Dean and Marlon Brando helped nurture their iconic status.
Michael says: 'I like to wear Levi's 501s. Their origins go back to the 19th Century, but it wasn't until the Fifties when more modern stitching and fitting of zippers as an option were introduced that they were turned into a fashion statement.'
For authenticity also check out selvages - white seams under the inside leg. These seams were discontinued by Levi's in 1982.
Also look at the details of rivets, location of pocket, stitching type and colour that changes over time.
Michael says: 'Stitching on the inside of the turn-ups might be white or white and red, depending on whether the denim came from the middle or at the edge of a roll --the red at the edge is often seen as better as the raw denim in this area is less treated and may be more hard-wearing.'
Rosemary Harden, 50, manager at the Fashion Museum in Bath, Somerset, says denim jeans became a vital part of Britain's wardrobe during the Seventies.
'Movie icons helped to give jeans international appeal, with Europeans adopting the fashion after seeing Hollywood stars on the screen,' she says. 'By the Seventies, jeans were commonplace.'
But she warns: 'Only buy jeans if you love wearing them. Middleaged people should be wary of combinations that make them look like Jeremy Clarkson.'
While vintage jeans can be found on internet sites such as eBay, specialist second-hand clothes stores may be a better starting place for the novice investor. Charity shops also occasionally throw up gems.
Be wary of fakes. If a vintage pair has a 'care label' inside them chances are that they are a forgery - they were not produced until much later.
?? One of a Kind vintage and secondhand clothing shop, 0207 792 5853; The Fashion Museum, 01225 477 173, fashionmuseum.co.uk.