Guitars are the loners of the musical industry. If they haven't been hurled over footlights, they've been abandoned under a bed by an amateur with blistered fingers. But, as John Windsor reports, these mistreated instruments are now in demand as investments.

Bonhams held its first guitars-only auction in June, the only one in London, and its second is next Thursday (11am). Saleroom debuts dedicated to a single commodity are instructive market-makers: they tend to go either through the roof or the floor. Among stringed instruments, the auction market for guitars is the rawest and most capricious.

Whereas violins, especially well-used and cared-for concert and music- school instruments in the pounds 1,000-pounds 10,000 range, sell at auction in their hundreds, guitars are mainly solo instruments. You never quite know where they've been.

Most change hands in private deals or are sold by dealers in shops or at fairs, where buyers who intend playing them can question the vendors. It is only collectable "association" guitars that belonged to pop stars that sell best at auction.

That Fender Stratocaster may be shattered, but at least you can read in the catalogue that Jimi Hendrix shattered it. As it happened, Bonhams' first guitar sale flopped. Of the 125 lots, only 33 sold. In an established market, an auctioneer turning in such a disastrous result would resign. But Bonhams' Jim Westbrook, a 38-year-old guitar teacher with 50 pupils in Brighton who had pitched Bonhams the idea of guitar sales, is undeterred, even chipper. He is building up a database of his target market - guitar players and teachers. They showed up in disappointingly small numbers in June. The sale was packed with bargain-hunting dealers, who were baulked by his bullish reserves, and by trendy young voyeurs, some unable to tell an electric Gibson from a classical Hauser at 20 paces. Several classical guitars by living makers, having failed to sell in the first sale, are back in next week's, this time with more modest estimates. This is the soft underbelly of the guitar market.

So why join a waiting list for new ones or pay a retail dealer top whack? Snap them up before more buyers enter the market. A classical guitar made in 1986 by Edward Jones of Oxford, who started his career making harpsichords and signs himself "luthier" on the label, failed to sell at an estimated pounds 1,100-pounds 1,200 in June and is back with a lower estimate: pounds 850-pounds 1,000. You might pay pounds 1,500 in a shop for this fine specimen in prized Brazilian rosewood. Try it out at one of the pre-sale views. A 1984 classical guitar by the London maker Trevor Semple, in Honduras rosewood with mosaic butterfly decoration, was unwanted at pounds 1,000-pounds 1,500 last time round. Now it is pounds 800- pounds 1,000. Likely shop price: pounds 1,800. Appearing for the first time at auction: a 1990 classical guitar by David Whiteman of Brighton. He learned guitar- making at the old

London College of Furniture, whose world-famous name has been absorbed by the London Guildhall University, and is now a senior lecturer in guitar- making there.

He has been hailed by Tim Miklaucic, one of America's biggest classical guitar dealers, as "one of the best new makers I've found in England". The Whiteman, in Brazilian rosewood, is estimated pounds 700-pounds 1,000. Likely shop price: pounds 1,500.

Mr Westbrook will tell you that it has lain under the bed of its owner, who never got round to learning to play. He does find out where they've been. These fine contemporary instruments will rise in price.

As for investing in the rest: watch it. It probably takes less time to learn to play the guitar than to bone up on the sort of minutiae that can make a ten-fold difference in value. Each kind of guitar - 18th and 19th century classical, contemporary classical, acoustic, electric, archtop, slide - is virtually a different commodity. Each has its own arcana and anecdote. Mr Westbrook is one of the few who can tell the difference between a modern classical Jose Ramirez 1A and 2A. The 2A is of second quality, defined perhaps by a mere slip of the chisel, now burred over.

Even the renowned MT, who made guitars for Ramirez of Madrid in the Sixties, could occasionally turn out a 2A. But if you know that Segovia favoured guitars made by MT - that's Mariano Tezanos Castro, to aficionados - then you will not be put off if you find his initials written inside a guitar said to be by Ramirez.

On the other hand, PB (Paulino Bernabe) left Ramirez and became famous without Segovia's patronage. It can be confusing. Sometimes the makers simply forgot to write their initials. A Ramirez 1A in next week's sale has no initials but is estimated pounds 1,200-pounds 1,600. Sotheby's sold a 1A Ramirez without initials for pounds 1,620 in its musical instrument sale this week.

Famous players do add value. Julian Bream popularised Hauser and the English maker Kevin Aram acquired a long waiting list for his guitars when news leaked out that Bream had taken to them: one sold for pounds 2,300 in Bonhams' June sale (estimate pounds 2,000-pounds 2,200). Investors should also look at the electric prototype and two first-off production models made since 1989 by Patrick Eggle on his farm near St Albans, with the help of funds from the Prince's Trust. Cliff Richard, Jethro Tull and the Shamen are among pop names who have played them on stage. Estimates pounds 450-pounds 650 to pounds 3,000-pounds 4,000.

The auction price record for a guitar is still the pounds 198,000 paid at Sotheby's in 1990 for a 1968 electric Fender Stratocaster. Fenders made after 1965, when Leo Fender sold out to the CBS record company, are worth less. But this one happened to have been played by Jimi Hendrix at Woodstock.

On the other hand, John Lennon played Rickenbackers. How many people have heard of them? As for the top-priced Gibson Les Paul Standard, pioneer solid-body electric of 1958-60, what big names played it, apart from Eric Clapton? Only about 1,000 were made. It commands pounds 20,000-pounds 100,000 and is still rising.

Non-association pre-1965 Stratocaster prices have risen to pounds 4,000-pounds 10,000, too expensive for some collectors, who are now pushing up prices of Seventies models (Hendrix played those, too). There is a Seventies Stratocaster in next week's sale estimated at a mere pounds 300-pounds 400.

The nearest thing to pop collectables in the sale are three Fender Stratocasters from a limited edition of 40 made for Stratocaster's 1954 40th anniversary film, Curves, Contours and Bodyhorns. A signed one is estimated pounds 30,000- pounds 40,000.

Mr Westbrook refused to let Bonhams' rock and pop memorabilia department hijack them. "They're the finest Stratocasters you can buy," he said.

Bonhams Fine and Rare Guitars, Thursday, 11am. Viewing from tomorrow, 11am. Jim Westbrook, phone 01273 328 118.