Some say it was inspired by a lively bunch of Madeiran cabinet-makers jobbing as braguina virtuosos. Others claim it was given to a British serviceman named Edward Purvis who would hop and jig while he played.

Whatever, sometime in late 19th-century Hawaii the braguina, a small, four-stringed chordophone from Madeira, spawned another similar instrument dubbed the “ukulele” by locals, who thought its quick-fire sound mimicked a “dancing flea”. The name stuck, and with it a certain tradition of mockery. The ukulele has spread throughout the world, but the instrument has remained poised on the brink of cultural acceptance – and for many it is, by nature, irrevocably comic.

Throughout the 20th century the ukulele enjoyed brief moments of fame. The Panama-Pacific Exposition of 1915 inspired a fad in the US, and popular black musicians and Tin Pan Alley songwriters carried the instrument well into the 1930s; for many people it was the signature sound of the Jazz Age. Thereafter, however, it has often been dismissed as the preserve of eccentrics and shady aficionados. George Formby’s buck teeth and smutty humour had a limited appeal – his song “With My Little Stick of Brighton Rock” was deemed too risqué for broadcast on the BBC during the 1940s (the mind boggles at the double entendre) – and likewise Tiny Tim, with his freak-show looks, exploited the ukulele for comic, rather than musical, effect.

Happily, the new champions of the instrument, The Ukulele Orchestra of Great Britain, has surpassed them both in terms of longevity, virtuosity and, by all accounts, sex appeal. “In 1985 we played a gig in the local pub in Borough, London, thinking it was a one-off thing,” says director George Hinchcliffe (right) “but the audience were enthusiastic.” In those days ukulele enthusiasts were a peculiar breed – “sort of Masonic, with blazers and ties” – but over the last 25 years their fan base has expanded, and is sure to increase further when the eight-strong group play at their own Prom concert in London this month.

Some Prommers will be wondering how ukuleles crashed the party, but in many ways the instrument sums up the quintessence of Proms spirit, being both quirky and accessible. “I think it’s possible Roger Wright, the Proms supremo, is regretting his decision,” Hinchcliffe laughs. “I’m not sure if people are latching on to it because they think it’s completely risible, that Radio 3 have blotted their copy book, or whether they think it’s something of a novelty.”

As well as hits by The Who and the Sex Pistols the UOGB will be playing a range of classical excerpts, including Wagner’s “The Ride of the Valkyries”, and audience members are invited to bring along their own ukuleles for a mass rendition of Beethoven’s “Ode to Joy”. Anyone who is interested can follow online masterclasses on the BBC website, where band members explain how to tune the instrument, and the chord sequences for the piece. The orchestra has played with audiences of around 200 at gigs in Sweden and Japan, but with over 600 players already registered, this is likely to be its largest ensemble to date.

The UOGB’s usual repertoire ranges widely; a take on “The Good the Bad and the Ugly” might follow Nirvana’s grunge anthem “Smells Like Teen Spirit” or, a favourite at live performances, a swing version of Kate Bush’s “Wuthering Heights” complete with a scat-sung intro. Their witty, deadpan style and well-honed flippancy conceals a consummate skill, and the sophisticated sound they produce – both percussive and melodic – is at once hilarious and heartfelt. Each of the eight players enjoys a cult following and their fan site is alive with chatter: pleading appeals for a US tour, paeans to Jonty, “the hottest bass uke player ever” (it’s a high bar) and nerdy discussions about the comparative merits of Martin and Aquila strings.

Over the last few years there has been growing evidence to suggest that the ukulele is – whisper it – now in vogue. No longer confined to folk conventions they are proving popular at the big music festivals (the accessory of choice, along with fraying panama and a stubby) – and there’s nothing like Glastonbury for marking out the mainstream. Like the unlikely craze for knitting that has flourished in recent years, ukuleles have also enjoyed endorsement from film stars and fashionistas: Rosamund Pike claims to be learning and Clive Owen was spotted at a recent UOGB gig. Even Tony Blair was snapped strumming a ukulele while on holiday in Barbados.

Which makes you wonder: are ukuleles simply being used as posing props or are people actually learning to play? Stockists such as London’s Duke of Uke emporium have reported a rapid increase in instrument sales over the last few years, and some people are now suggesting that they replace recorders as the classroom instrument of choice. It makes sense: ukuleles are cheap and portable, and the strings are close enough for small hands. “We’ve done workshops in schools,” Hinchcliffe says, “but I’m a bit worried about the recorder players and teachers; I’d hate to get labelled as being part of a movement to replace recorders.”

Is he reluctant for the ukulele to adopt such a conventional role? Enthusiasts might prefer that these instruments remain a little outré and uncool, but their rise now seems inexorable. For the UOGB – and ukuleles generally – this is quite a summer: last month, Hinchcliffe tells me, the band had their first pair of knickers thrown on stage (“they were enormously large and pink with nice frilly bits round the edge”) and in just over a week they make their Proms debut. I’m not sure which is the greater milestone.

The UOGB plays at the BBC Proms, Royal Albert Hall, London on August 18 www.bbc.co.uk/proms/2009