"My father was just a born entertainer," says Brennan. "He came from the old-school show band era and musicals and when the dance hall culture died down here in Ireland and everything moved into the taverns, he decided he wanted to open a pub."

Leo never drank or smoked in his life, she says, but it was where he wanted to be. He had eight kids and one on the way when he opened the pub in 1968.

"Never in his wildest dreams did he think the pub would be such a success," she said.

Brennan remembers nights up on stage with her siblings: "We could all sing and perform," she says.

"The house was full of love and music, even before we moved into the pub, I remember hearing my father singing Elvis, Nat King Cole, the Everly Brothers. It was a really strange upbringing if you can imagine it because our first language is Gaelic, to hear our father rehearsing these popular songs in the parlour."

In 1973, Brennan and her brothers Ciaran and Pol, who were all still at school, performed with their uncles Noel and Padraig Brennan at the Letterkenny Folk Festival, winning with a song called Liza. Clannad was born.

Fifty years later they've sold more than 15 million records worldwide, winning a Grammy and a BAFTA award, as well as a BBC Radio 2 Lifetime Achievement Award in 2014. Their sister Enya played with them for a few years before heading off on her own solo career. She's the best-selling Irish solo artist in history, the second best selling act after U2.

Brennan said they never expected any of it. "When we did that first album in 1973 we just thought it would be a nice thing to show our grandchildren in years down the line, rather than thinking that we'd be going on our farewell tour 50 years later."

Clannad has toured Australia twice before, it's been 10 years since the last tour and this will be their first since founding members Noel and Padraig died in 2016 and 2022 respectively. Australia will be one of the last places they'll play live before they "call it a day on a high", says Brennan.

She's warmed by the fact I'm a long-time fan. I had their collaboration with U2's Bono, the single In a Lifetime, on vinyl. The song Theme from Harry's Game, which I came to via the film Patriot Games, but which was originally written for a television series about The Troubles in Northern Ireland in 1982, appeared in my Spotifty top songs for 2022 playlist.

But it's been hard to describe their sound to colleagues who were unfamiliar with them. Brennan says they've faced the same problem for 50 years.

"It's not traditional, or folk, there's a real Celtic sound to it all," she says, at the same time acknowledging the influences of the harmonies of The Beach Boys and The Mamas and The Papas that her father listened to. "I remember some of the first performances at the pub would involve us singing a couple of Gaelic songs and then a couple from The Beatles, it was often a real mismatch. But we were drawn to the Gaelic songs, and rearranging them in our kind of way."

In 1986 Clannad had a half-written song stirring and on a whim they asked Bono if he'd like to collaborate with them. After the first evening's recording, an electrical storm raged over Dublin and the song changed tack. Brennan remembers it as one of the most remarkable things she's ever seen in a recording studio. Bono says Brennan's voice was one of the most magical he had ever heard.

Their music has appeared on many soundtracks such as Harry's Game, Robin of Sherwood and The Last of the Mohicans, where Brennan sings in English, Mohican and Cherokee. Some people say James Horner's Titanic score was inspired by Clannad. "We developed a new sound and a lot of people have jumped on it over the years," she says. "It's a huge respect to your work when people copy you, I suppose."

To coincide with the farewell tour, BMG Records have released In a Lifetime Anthology, a multi-format, career-spanning compilation. The live shows will see Clannad performing songs from the anthology, all their favourites.

At 70, Brennan isn't looking to take it easy when the tour's over. She has solo plans in the pipeline. In her 2000 autobiography The Otherside of the Rainbow she talked about the part drugs and alcohol played in her life. Now she enjoys walking on the beaches of Donegal, along the windswept shores of the Atlantic. She loves painting, two of her solo albums, Canvas and Timeless feature her own artwork. Her Christian faith is very important to her.

And music will remain in her life forever, she says. She still heads back to her father's pub to perform once a month, if her brothers and sisters are around you're in for a right treat. Her father passed away six years ago but busloads of people still come in, hoping to hear them.

"Our parents gave us this wonderful opportunity, this wonderful gift, and if we've managed to share a little bit of that over the years then we're happy."