Return of the last Tipperary balladeer

Liam Clancy, the last surviving brother and, at 72, the youngest, recalls the matching sweaters as their manager's idea. The brothers themselves had only one real ambition: to have fun.

"We'd really come to America to be actors," he says. "But we found we were being offered more singing jobs, which paid better, so we decided to give it six months, just focus on the music for that time, then go back to the real job of acting. If we'd been serious about it, it would never have worked."

It's hard to conceive nowadays how huge and influential the Clancys and Makem were. Already a popular draw around the New York clubs, the band went stratospheric following their 1961 appearance on The Ed Sullivan Show, extended from three to 14 minutes when another act cancelled. Among the show's 80 million viewers that night was Columbia Records' legendary talent scout John Hammond. He signed Bob Dylan to the label and promptly offered the Clancys a five-year deal, with a $100,000 advance. It was an immense sum at the time, and utterly unheard-of for a folk group. The following year they sold out Carnegie Hall and later played to an open-air crowd of 45,000 in Boston - this in the days before sound systems even existed to cope with concerts of that size.

As to influence, no less an authority than Dylan himself cites Liam Clancy as "the best ballad singer I ever heard in my life" and as the source of several folk-songs he adapted into compositions including Ramblin' Gamblin' Willie, Endless Farewell and With God On Our Side. The friendship between the two continues to this day, their most recent encounter being after Dylan's last gig at Madison Square Garden.

"Everyone ended up at Tommy Makem's bar - George Harrison was there, Ronnie Wood, Neil Young, Tom Petty, all these people, and Bob and I were just in a huddle in the corner," recalls Clancy, who features in Martin Scorsese's celebrated Dylan documentary, No Direction Home. "I think he was longing to speak to someone from his reality days, rather than from the rock'n'roll madness, so we just talked about all the characters we knew back then, old girlfriends and so on.

"At one point, I mentioned that I'd been thinking of recording a couple of his songs. He seemed really pleased, which took me aback a bit, and he said to me, Man, you just don't get it, do you? You're my hero.' Then later on I shoved a guitar into his hand, and he ended up singing Roddy McCorley, one of the old Clancy hits, with everyone joining in."

Back in Ireland, the Clancys' impact was nothing short of revolutionary, thanks not only to their exuberant reinvention of songs long associated with poverty and subjugation, but their slick, telegenic image and professional stagecraft. Bill Smith, co-founder of The Corries, has credited the Clancys and Makem with "opening a door where no-one even knew a door existed". It was a portal to a new folk era through which bands such as The Corries, The Dubliners and The McCalmans soon followed, along with countless lesser imitators who together spawned during the "ballad boom" of the 1960s. For Liam Clancy, who arrived in the US as a 19-year-old fresh from rural Tipperary, those early years were "like suddenly finding myself in the middle of a really great party, that just went on and on and on".

With his actor brothers Paddy and Tom already living in New York, he'd been spirited there by the folk music-loving heiress Diane Guggenheim, who took a shine to Clancy when she met him on a song-collecting trip to Ireland. Enlisted as her assistant, he accompanied her on a visit to the renowned Armagh singer Sarah Makem - also the start of his lifelong friendship with her son, Tommy - and then to the US where Guggenheim, using the name Diane Hamilton, set about establishing the pioneering folk label Tradition Records. Meanwhile, Paddy and Tom set up a tab for Liam at Greenwich Village's famous White Horse Tavern. The brothers' singarounds with Makem there and at the Fifth Peg (later famous as Gerde's Folk City) soon began attracting a local audience, but with their sights still set on the theatre, as Liam recalls, they only began recording by way of a favour to Hamilton.

"Diane had set up this record label, and Paddy was running it, but they didn't actually have any records yet, so we basically made our first three albums so that Tradition had some catalogue. All sorts of people ended up on the label after that - Odetta, Alan Lomax, the Kentucky singer Jean Ritchie, Ewan MacColl and AL Lloyd from Britain. Diane was really a key catalyst in the whole Greenwich Village scene taking off, and certainly in us ending up where we did."

In musical terms, however, it wasn't all that long before the Clancys and Makem became victims of their own success. Even as they strove to perfect their vocal interplay and develop their performances - which in the early days would often incorporate recitations of favourite poems and theatrical excerpts - the bandwagon was riding roughshod over their sound's finer points.

"As the crowds got bigger, the more raucous songs became the favourites, and all the subtleties we'd built in got forgotten," Clancy says. "The whole thing became a bit of a cliché - just rowdy, rowdy, rowdy all the time, and we all got disgusted with it."

Makem left the group in 1969 and Liam followed four years later. The pair reunited as a duo from 1975-86, scoring a major hit with Eric Bogle's anti-war anthem And the Band Played Waltzing Matilda, which topped the Irish charts in 1976. It also resolved Liam's then-considerable financial woes, arising from the Clancy Brothers' unpaid tax debts.

Clancy had learned the song from Scottish musician Archie Fisher - nowadays presenter of Radio Scotland's Travelling Folk - who will be an honoured guest at his forthcoming Celtic Connections concert. "I can't wait to see Archie again," Clancy says. "I still have him to thank for building my house."

Since parting ways with Makem, Liam has performed in various Clancy Brothers reunions. Elsewhere he has teamed up with his guitarist son Dónal - a member of the band Danú, who also feature in the Celtic Connections show - and singer-songwriter nephew Robbie O'Connell, as well as working solo. In 2002 he published the first volume of his autobiography, taking the story up to that landmark Ed Sullivan appearance. He is currently at work on the next instalment.

When our conversation strays almost inadvertently into politics it's clear that Clancy has little intention of mellowing with age.

"Today as much as it ever did, that song And The Band Played Waltzing Matilda articulates things I find very hard to put into words - like how intensely I feel about Bush and Cheney, for instance. I really believe they're evil people. They've steamrollered over democracy and decency while causing the deaths of countless innocents, all through manipulating by fear. They're just the dregs of humanity"

Even his concomitant hopes for the forthcoming US election are tempered by a chilling foreboding. "If Barack Obama steamrollers ahead to the presidency, as it looks like he might well do, I wouldn't be at all surprised if he was assassinated before taking power. I think the forces that killed Martin Luther King and the Kennedys are still there and still just as powerful, and they could well find a way to take him out."

On a happier note, however, Clancy is palpably excited about this week's Glasgow date, his first in Scotland for many years. And he is happier still to be performing with family, even in the absence of his brothers and Makem. "Seeing that lineage continue does help balance out the losses," he says. "I've seen so many endings - but also so many beginnings. You learn to grieve for a while at the endings, but then exult at the challenge of something new. I love that line of Bertolt Brecht's: With a man's dying breath, he must be prepared to make a fresh start'. That's definitely my attitude now."