Picasso? I'd rather have an Eames

Overall, big-name designers remain the safest - and most lucrative - bet. And, according to Jeremy Morrison, head of applied arts at Sotheby's Olympia, 'It's better to have one really good piece rather than five lesser ones - an early piece from the original production of a design will appreciate much faster than one produced later.'

Applied Arts and 20th Century Design, Sotheby's Olympia, 3 May; 020 7293 5000; www.sothebys.com

Rachel Harding works at Hemisphere Decorative Arts in Fulham Road, which sells Forties and Fifties design. She and her partner, Ron Wigham, collect mainly French post-War furniture.

'We began collecting vintage jewellery and watches 18 years ago,' says Harding. 'Soon after, we bought ceramics, then graduated to furniture. We started off buying Forties furniture - lots of ornate wrought-iron and leather. But we've since changed our taste to a more industrial, austere, Fifties style, which combined metal and wood.'

The couple's vast collection of French furniture includes desks, sideboards, coffee tables and lighting, but their favourite piece is the ultra-rare Mexique bookcase in the study, designed by French architects Charlotte Perriand and Jean Prouv?. One of a limited edition of 72, the bookcase was designed in 1953 for the student digs of several Paris universities. Made of pine, mahogany and metal, it has sliding doors with diamond-point texture (a surface faced with tiny, diamond-shaped points in relief), and was bought from Paris antique shop, Galerie 54. It comes in three colourways - red and yellow, blue and yellow, and red and blue - chosen by artist Sonia Delaunay (although its jazzily coloured rectangles recall a Mondrian canvas). Harding and Wigham wanted a blue and yellow one 'because the colours remind us of the sun and the sea. We love the fact that it's so versatile: it can be used as a bookshelf, to display ornaments or as a room divider - because it was designed by architects, it's got great proportions.'

'Prices of Prouv? pieces are going through the roof,' says Harding. 'Another Prouv? Mexique bookshelf recently sold at auction for £26,000. French design isn't extensively reissued, so when you buy French pieces by sought-after designers you're almost definitely buying an original, which increases its value.'

Alice Rawsthorn is the director of the Design Museum. She lives in Shoreditch, and collects anything from early-Eighties Ron Arad pieces to objects by new Parisian design stars, the Bouroullec brothers (now on show at the Design Museum until 16 June).

'When I was at Cambridge, I bought all my clothes second-hand and then started buying odd bits of furniture, mainly 20th-century modernist pieces. But, over the years, I've also bought furniture that was contemporary at the time.'

In the early Eighties, she bought pieces in the hi-tech, industrial style fashionable at the time, such as Ron Arad's iconic Round Rail bed, which incorporated his Key Klamp scaffolding railings. By the late Eighties, she'd moved on to pieces by Tom Dixon, namely his 1988 'S' chair with a rush seat (still her desk chair today). In the early Nineties, Rawsthorn worked in Paris as a foreign correspondent and snapped up Twenties pieces at the famous March? aux Puces, including 'chandeliers that preceded - and, in their simplicity, anticipated - Art Deco'. She also procured, 'purely as an investment', some highly collectable Deco pieces by Jean Dunand and Emile-Jacques Ruhlmann. The latter was a very prescient buy - minor Ruhlmann pieces are now fetching £20,000 to £30,000, while major pieces go for £500,000 plus.

While in Paris, she also befriended the then little-known London-based designer Marc Newson. 'Over the years, he's given me lots of pieces. Now they're incredibly collectable. Ironically, he can't get hold of lots of his early, limited-edition pieces because they're in the hands of collectors.'They are also now fetching £20,000 to £30,000 each.

Two particularly cherished pieces of hers - which are bound to shoot up in value - are a pair of carafes designed by Ronan Bouroullec, one of the two Parisian brothers, who are becoming France's most promising designers since Philippe Starck. 'I've collected so much stuff I've had to put a lot of it into storage,' continues Rawsthorn, who once bought Marc Jacobs' entire grunge collection designed in the early Nineties for Perry Ellis, because she knew this landmark in fashion history would inevitably rise in value. 'But if I do put things in storage, they have to be pieces I think will appreciate in value in the future.' But a passion for collecting is as important a part of the equation: 'They've got to be objects I really like in the first place, too.'

David Morris manages Soho casting studio Kitsch. He invests in British post-War design and a smattering of British art from the same era.

'I'm attracted to British design because it's very underrated. But people are waking up to British design because it's cheaper than French and American furniture but it's still an investment.'

Morris's favourite piece is a three-piece suite by Ernest Race, upholstered in grape-coloured wool with black leather arms. Designed in 1956 for the ocean liner Oriana, it is all the more rare for having been a one-off commission. 'I paid £4,500 for it three years ago,' says Morris. He is reluctant to reveal its value, such is the competition between collectors, but a piece like this would now fetch around £8,000.

Morris also owns two standard lights by esoteric Fifties husband-and-wife team John and Sylvia Reid, bought from Target Gallery in Fitzrovia. He also has a very rare Wells Coates desk, designed in the Thirties, with drawers covered in navy blue kid leather. 'It cost me £800, two and a half years ago.' Another find is a ceramic lion and unicorn designed by another Brit couple, Richard and Susan Parkinson, for the Coronation. Emblazoned with the 'ER' and '1953', these are very rare. 'I paid £650 for them a year ago. Jeff Rayner, the owner of Target Gallery, was offered £700 for a pair recently, even though one had a broken foot and neither was decorated with ER or 1953.' Morris also has a rare Sixties ashtray by St Ives pottery Troika, and drawings by Damien Hirst and Lucien Freud, which complement his post-War British design.

So what are his tips for investing? 'Buy the very best design you can afford, rather than buying cheaper things in a scattergun way. It will really pay off. I'm happy to do this now and then, even if it means living on baked beans on toast for two months to compensate.'