Sting's next album - due in October - dispenses with unit-shifting pop in favour of an album of 16th-century lute music written by the composer John Dowland. According to Sting, someone recently gave him a lute, which reminded him that Elizabethan music had "haunted" him for decades. You'd never guess that from Message in a Bottle. Ex-Fairport Convention man Richard Thompson - recently named the 19th greatest guitarist of all time by Rolling Stone - has just released 1,000 Years of Popular Music, an absorbing collection of songs, dating from an unlikely Britney Spears cover to as far back as 1260. Then there's Ritchie Blackmore, who once rocked hard in Deep Purple and Rainbow but now surrounds himself with "minstrels" with names such as Bard David of Larchmont, and insists that all band members wear tights. Which might well be an increasingly common sight over the next year. Candice Night - who gently sings over Blackmore's mandola in Blackmore's Night - suggests that medieval music is the latest form of escapism. "A lot of people are drawn to the jousting, but for us the most exciting thing is being dressed in the garb, drinking meade while Ritchie plays his mandola," she says. "It's a way of transporting yourself to a simpler, more magical time." Night met Blackmore when she was just 18 (she's now 34, he 61) and has completely bought into the lifestyle. Blackmore's Night play gigs at 12th-century castles and stay in "air-conditioned, castle hotels".

Others argue that looking backwards could provide a lifeline for pop. When Thompson was growing up in the 1960s, he listened to everything from jazz to folk to the Who, and he laments the way the industry has "narrowed everything down to something salable and palatable. Sometimes, the baby is thrown out with the bath water," he argues. "Great ideas, tunes, rhythms, styles get left in the dust of history. So let's have a look back there and see what we can do with it."

Some of the music backs him up. Pointy shoes or not, Circulus have stumbled across a new type of psychedelia by mixing 12th-century chamber music with synthesisers and guitars. American band Espers' eponymous album, Espers II, due in July, features fragile otherworldly folk songs played on doumbek and dholak - the music is dark, powerful and pure. Thompson maintains that olde instruments such as the crumhorn and lizard (a tenor cornett) have the "earthy, crude" power now lost from modern rock 'n' roll. "These are not sweet-sounding, they are instruments with attitude," he says. "Almost punk."

One of the highlights of Thompson's album is King Henry, a 15th-century traditional song. Take away the curious lyrics ("The King called out for his luvverly page") and rustic earthiness and Thompson is right to view it as a simply brilliant pop song. "There's nothing extreme about this," he says. "Pop began closer to 1055 than 1955. The structure of, say, a 15th-century dance tune, is remarkably similar to Tamla Motown."

The instrumentation, of course, is different, and bands vary in their approaches, from covering old songs to weaving influences into new ones. Thompson thinks Sting's idea of covering John Dowland is a good one, because "he was probably the first great singer-songwriter". But opinion differs on whether the ex-Policeman could actually play a lute. Dr William Flynn at Leeds University's medieval studies department says: "It was an early form of guitar, but they're extremely difficult to master. Sting's a guitarist, so he could get started. He could probably make a sound."

Such dabbling isn't new. Sixties singer-songwriter David Munrow was probably the first to experiment with "early music", and bands such as Pentangle, Midwinter, Stone Angel and Gryphon made some groundbreaking music by fusing medieval sounds with psychedelic rock (and modelling Charles II-era hairstyles). Folkies (and folk-rockers such as Fairport Convention) have a long tradition of courtly love songs. Night points out that the medieval pop influence goes deeper than we think, explaining that her partner came up with the immortal riff for Deep Purple's Smoke on the Water after stumbling across the BBC's The Wives of Henry VIII, and later adapting medieval scales. "The same bombastic riff will translate from being played on crumhorns, shawms and sackbutts to electric guitar." These days, Renaissance music is "all Ritchie listens to at home", she says, although he still rocks out by playing an amplified hurdy-gurdy at 3am - presumably to the delight of the neighbours.

However serious these artists are about the technicalities of the music, it's true that they're also providing a sense of fun often missing from formulaic pop and endless clones of Franz Ferdinand - who, insists Tyack, "would sound much better with a harpsichord". Katherine Blake fronts the Mediaeval Baebes, described on their website as "provocative maidens singing songs from an age of innocence" - probably not what Blake's tutors at the Purcell School of Music had in mind. Still, she gets to dress as a princess ("crucial for getting into the right frame of mind"), and will appear at next month's Joust festival, which promises "medieval mayhem" and games such as Pelt the Peasant. The Baebes are often led on stage by men in suits of armour. "When they get stuck into the mead tent," sighs Blake, "they start brandishing their swords."

Blake insists she spends "hours" poring over medieval texts, but authenticity is a thorny subject, not least because even experts argue over how early music sounded. Blackmore's Night are at their best when sounding genuinely aged: when they mix Renaissance sounds with soft rock, they sound like a Eurovision entry.

Where all this will lead is anyone's guess. Sting in armour? Pete Doherty in minstrel's bells? Perhaps Thompson is right to argue that "sometimes, you have to go far back to look forward" and some amazing music will result. Blake predicts a "manufactured medieval band", while Tyack is absorbed by the thought of "tricking time" and getting into the heads of musicians who 400 years ago were "seeking solace from pestilence, just as we escape the internet and Tesco."

Dr Flynn sees trouble ahead for Circulus. "Those long pointy shoes are historically accurate," he says. "But you had to be pretty well-off to wear them. You'd need servants to do all your fetching and carrying, because if you walked in them for long you'd fall flat on your face." As for Blake's own group, they plan to stick around long enough to call themselves the Medieval Crones

The ignoble history of medieval-dabbling pop

Richard Thompson Sumer Is Icumen In (on 1,000 Years of Popular Music) Wonderfully earthy folk tune written in 1260. Probably originally owned by William of Winchester, a "lover of music and worldly things" who, Thompson notes, "was brought before the Bishop of Hereford for incontinence with several women".

Dead Can Dance Into the Labyrinth 4AD-label trendies' 1993 venture into medieval goth.

Blackmore's Night I Still Remember (from Fires at Midnight) Haunting 2001 tune reminiscent of late 1970s folk princess Sandy Denny and. Period garb essential, fairy's wings optional.

Herman's Hermits I Am Henry VIII, I Am Sixties Merseybeat-y pop song that wrongly suggests the sire was alive and beheading in 1965.

Rainbow Sixteenth Century Greensleeves (from Ritchie Blackmore's Rainbow, 1975) Classic hard rock: definitive quasi-medieval metal silliness. "It's been only an hour/ Since he locked her in the tower." Need we say more?

Donovan Hurdy Gurdy Man Travelling minstrel Donovan Leitch's medieval fetish began in 1966 with Guinevere, but this, from 1967, is sillier. Lovely tune, though.

Jethro Tull The Broadsword and the Beast (1982) No more sensible than you'd expect from a band fronted by a flute-playing man in a codpiece. The cover depicts vocalist Ian Anderson as an elf.

Rick Wakeman The Myths and Legends of King Arthur and the Knights of the Round Table (1975) Tour de force of unmitigated medieval costume pomp rock keyboard lunacy and lyrics such as: "Fight! Fight!"

· Richard Thompson's 1,000 Years of Popular Music is out now on Cooking Vinyl.