Time was when Christmas stockings had, as well as the mandatory apple and orange, a tin whistle sticking out of them.

Time was when Christmas stockings had, as well as the mandatory apple and orange, a tin whistle sticking out of them. I know because I used to sell them, the Clarke's black-and-gold C whistle and the slightly more upmarket Generation flageolet, whose availability in every key didn't stop it being referred to by Christmas shoppers as just a novelty, as if something that small and that cheap could never be considered a real instrument.

Mary Bergin doesn't remember if she got her first whistle in her stocking, although she does remember her chosen instrument being knocked as a novelty - once even by a bloke in a Dublin music shop, may he hang his head in shame - and feeling quite insulted. She didn't set out to get revenge but if she had, she could hardly have extracted it with more style. Because Mary Bergin, for those who don't know her, is a name spoken with awe among traditional musicians across the world. In her hands, the tin whistle is as expressive and personal as any instrument in the classical or traditional canons.

When her first album, Feadoga Stain (or Tin Whistle), came out in the late 1970s, it became an inspiration as well as the gold standard for budding and accomplished players alike. It was also quite handy for playing to non-believers, whose attitude towards the tin whistle would be swiftly revised by Bergin's triple Kleenex slow airs and Irish-stream-in-spate-style jigs, reels and hornpipes.

Tin whistle legend status wasn't quite what Bergin's parents had in mind for her when they first noticed her ability to join in at their regular family get-togethers, where the songs of Irish tenor John McCormack would mingle with classical violin pieces, jazz and Irish traditional music.

"I suppose they thought I had a talent that might be applied to the piano or the fiddle," she says. "But when I tried those, I didn't have much luck with my teachers. The chap who gave me piano lessons used to sit and say the Rosary all the time I was playing. He was a really talented man and played the organ in one of the big Dublin churches, but he was troubled, poor soul. Or maybe I troubled him and drove him nuts because I had a good ear and if you played me a tune once, I had it and this made me lazy. He'd get me to play something and stop me and ask where I was on the stave - and I hadn't a clue because I was playing by ear. So after about nine months we parted company."

Her fiddle teacher, an old man of the road whom Bergin's parents sought to help by giving him a few bob to give their children music lessons, proved unable to impart his knowledge. The fiddle itself played a big part in Bergin's development, though. In fact, with the exception perhaps of the late Willie Clancy - uilleann piper supreme, font of folkloric wisdom and all-round character - whom Bergin's family befriended on their camping holidays in County Clare, it was fiddlers, rather than other whistle players, who influenced her most.

"My dad played the melodeon and he used to play tunes really slowly at first, so that I could pick them up," she says. "But once I knew a few tunes, I used to listen to these old scratchy fiddlers. They literally couldn't tell one note from another, but they had great rhythm and I've always thought that that's what music is all about, and no amount of ornamentation will make up for it."

In her teens Bergin competed at fleadhs, an experience she pooh-poohs as an excuse for the family to get out of Dublin and for her to play sessions backstage with fellow competitors, who didn't even wait to see who had won. She's being too modest because her name's on the All-Ireland championship cup, as a subsequent winner, Cherish the Ladies' Joannie Madden will tell you with glee.

Bergin was and still is, she maintains, too ill-disciplined to play the required pieces exactly as the judges would want to hear them. "I just play what comes out," she says. "This can backfire, I know, because when I've been teaching, people will say, I'd love to learn that tune. So I'll put it on a tape for them and they'll say, But that's nothing like what you played the first time. I'm not a great one for musical grades or competitions, really, although I do sometimes encourage pupils to go in for competitions so they can get used to playing in front of an audience. Some people need that kind of goal, but I worry they might lose the spontaneity that makes music exciting."

Ill-disciplined or not, by the time she left school and was doing the rounds of Dublin's traditional music haunts of the late 1960s and early 1970s, she was being invited to play in ceili bands and was soon appearing at festivals. Alec Finn and Johnny McDonagh, bouzouki player and bodhran master respectively of folk band De Dannan, persuaded her to make her base in Galway, where she still lives, and as well as bringing her into the band briefly, they accompanied her on the aforementioned Feadoga Stain album.

Another group, the baroque music meets the Irish tradition-styled Dordan, proved a more lasting vehicle for Bergin's talents before she settled into a routine of combining teaching work in Galway with gigging and tours at weekends and out-of-term time.

Right now, as she looks forward to her return to Glasgow to take part in the tenth memorial concert for the city's great Irish music champion, the late Jimmy McHugh, she's finally seeing a project that began 20 years ago, the Mary Bergin Tin Whistle Tutor Book, heading towards completion.

"I was doing a lot of teaching that involved travelling, sometimes just over to the Arran Islands but also to Sweden and Denmark. I was finally persuaded this was madness and that, instead, I should write a step-by-step tutor, from beginner through to advanced, two volumes, illustrated CDs the works. It's due in the summer - and I'm having to get a website, and it's scary because I've never had a plan. I've always just done and played what felt natural."

Mary Bergin appears at the Jimmy McHugh Memorial Concert, Woodside Halls, Glasgow, on Saturday, January 10. Further information from www.jimmymchugh.com