Imagine a middle-aged, bearded man sitting on a stool, lute on his knee. He is singing a ballad in Olde English, his voice a gentle whisper as delicate as the plucking of his stringed instrument.

Behind him a pale, tall woman with knee-length hair plays long, incomprehensible passages of music on her flute. A near-supernaturally hairy man wearing thick glasses bangs the drum at a slow, steady rhythm to complete the line-up.

Ye, my friend, have just conjured up a stereotypical portrait of folk music. Much in the same way that people label jazz as talented people mucking around with wind instruments, or indie music as whining, skinny white boys complaining about middle-class dilemmas, folk has always been boxed as slightly dull, meandering music tied to tired traditions.

It's a preconception that Fairport Convention have gone a long way to dispelling. Since their birth in the mid-Sixties, the band have allowed the familiar template of folk music to be both tweaked and transformed by the sounds of progress. They are widely lauded as the inventors of British folk-rock and, alongside artists such as Nick Drake and Bob Dylan, we can thank them for the raft of acoustic singer-songwriters (many of whom owe a huge debt to folk music) who now fill our charts. Not a time to ask: Fairport Who?' Simon Nicol, who originally hails from Muswell Hill, is a founder member and rhythm guitarist of the group.

"When I was growing up in the Sixties I would listen to all sorts of music," he said. "But at that time there only seemed to be two schools of folk. The agricultural, academic approach, sung with one finger in the ear, performing the music as should be done.' It was keeping folk music under glass. Then there were the more politically motivated, left-wing singers. There were no bands.' Now folk is more inclusive, with an anything goes' attitude that allows us to stretch out musically. There is less tutting nowadays, as people are starting to realise this music is indestructible."

Fairport Convention began as a group of friends and musicians convening at Fairport, Simon's nondescript house at the corner of Fortis Green and Fortismere Avenue. The early days were buoyed by experimental ideas in an era where boundaries were only created to be pushed. Bob Dylan was plugging in his electric guitar, The Byrds were mixing rock with country, and Joni Mitchell was blazing a trail for female singer-songwriters. The small band of forward-thinking folkies' at Fairport found themselves in an atmosphere of openness where the world was willing to embrace their music.

"I had a guitar and I knew about four or five chords,"said Simon. "We all knew a little bit of music. We were drawn together by folk music and from that point things seemed to move very quickly. We were professional within no time".

The band found itself subject to change in personnel during its first few years a recurrent theme in the group's history. Alumni include Richard Thompson, who along with wife Linda has had decades of success outside the band; singer Sandy Denny, a major influence of modern day artists such as Beth Orton; and Ashley Tyger' Hutchings, who went on to form Steeleye Span.

All three were present in the late Sixties as the band began to gain momentum through word-of-mouth, especially through good notices from BBC Radio 1 DJ John Peel. Their combination of Californian-style harmonies and strong acoustic melodies on top of the widely-recognised folk format gave them hits in their first three albums, Fairport Convention (1968) and What We Did On Our Holidays and Unhalfbricking (both 1969).

One fatal moment changed the landscape of their success completely. The band were on their way home from a gig in Birmingham when their van crashed on the M1. Drummer Martin Lamble, just 19, and Thompson's girlfriend Jeanne Franklyn, died. The rest of the band were injured, some more seriously than others, but all had suffered emotional damage that would take far longer to heal.

From the seeds of disaster came their most famous work, Liege and Lief, which was recorded in the wake of the accident.

"The accident was a hugely significant event, although it is water under the bridge and I don't like to dwell on it," said Simon. "But we had to pull together afterwards, and perhaps that was what made Liege and Lief a seminal record. It was a watershed."

Yet despite the success of the record, divisions had formed within the band and the innocent curiosity of the sessions at Fairport had been replaced by something altogether darker.

Hutchings left the band, followed by Denny. Thompson departed soon after, and even Nicol walked out for a short time. Nick Drake, the folk legend who had also performed with the band, died in 1974.

The band's output became patchy, showing flashes of the old brilliance, but not enough to keep them going. Throughout the 1970s, the record-buying public lost its taste for folk as new, louder, more exciting genres of music came to the fore. Without a record deal, Fairport Convention were left in the wilderness and didn't have the ideas to get themselves out. They split in 1979.

Since their subsequent reformation in 1985, Fairport Convention have been recognised on both sides of the Atlantic as a pioneering force in music. They still continue to produce albums at regular intervals, albeit with a hugely changed line-up. Only Simon remains from the original incarnation. Bassist Dave Pegg, who joined the group in 1969, is the only other member who enjoyed the band's heyday.

They play at Barnet Folk Club in November, only a few miles away from the small house where it all began. Fairport itself still stands, even if the group of friends who began there have found the structures of life itself are not always so solid.

"I'm not sure how long for this world it is, actually," said Nicol. "I've heard it may be due up this year, replaced by something or other. I was quite hoping we would have a blue plaque."

* Fairport Convention play Barnet Folk Club at the artsdepot, Nether Street, North Finchley, on Thursday, November 24, at 8pm. Call 020 8369 5454 for further information.