Lead vocalist Heather Findlay has left for pastures solo after 13 years, but the newly released album Go Well Diamond Heart represents a new beginning, one where backing vocalist Olivia Sparnenn steps into the spotlight alongside founder, guitarist and fellow singer Bryan Josh.

The first chance to see the reconfigured Mostly Autumn on home soil comes next Saturday night (DEC 4) at the Grand Opera House.

“From my point of view, it was very sad when Heather decided to do her own thing, make her own albums, but the good thing is that Olivia has been with us for five years,” says Bryan.

“We had a taster of her lead-singing abilities when she stepped in when Heather couldn’t do some shows abroad, and she fronted the band really well. She’s a phenomenal talent and a lot of fans were pleased that it was a change from within.”

The band undertook a fortnight-long “intermediate tour” last spring, but the autumn dates are viewed as the line in the sand. “This tour is the proper re-start with Olivia fronting the band with the new songs,” says Bryan.

“It’s been brilliant so far on tour; it’s gone down really well,” says Olivia. “The fans have been great and the feedback has been fantastic.”

“It’s great too that Heather is continuing with her own material, so that’s good news for the fans – and we’re all on good terms with Heather,” says Bryan. “We baby-sit for her when we can!”

He is becoming accustomed to the new Mostly Autumn. “It’s been different! When Heather did decide to leave the band, it was not just 13 years of writing and gigging together all over the world, but it was a long time of being together, but though it could never be the same and never sound the same, it’s still Mostly Autumn,” says Bryan.

“It has a new sound to it that’s refreshing. Maybe we needed a kick-start and a fresh beginning. There’s been no animosity; things don’t stay the same; we move on, and Olivia has done tremendously well.”

The new album, the band’s eighth studio set, has a title with echoes of Shine On You Crazy Diamond, Pink Floyd’s tribute to former member Syd Barrett. In this instance, Go Well Diamond Heart reflects on the death of another Floyd musician, Rick Wright, expressly on the song Violet Skies, while the title track takes its inspiration from the story of Yorkshire soldier Lance Bombardier Ben Parkinson, who is believed to be the most wounded soldier to survive his injuries in the ongoing Afghanistan campaign.

Ben, who lost both legs and suffered brain damage in a landmine incident in 2007, was the guest of honour at Mostly Autumn’s concert at the Opera House last December. “We got to know Ben, and his indomitable spirit was a strong part of this album,” says Bryan.

“So the title song is a tribute to him. We’re not getting political and saying we’re pro-war but we admire people like Ben who show such courage.”

The album opens with a tribute of a different kind, more an appreciation, to mark the closing of one chapter in Mostly Autumn’s history and the opening of a new one. “Because this album is a big album for us and a big change, we wanted the first track to be an acknowledgement of that, so For All We Shared is about all we shared in the past with Heather, and Violet Skies [the second track] is partly about her leaving too, and then we move on into the next era,” says Bryan.

The song-writing for Go Well Diamond Heart mirrored past albums. “As it usually does, it involved me hiring a cottage in the Lakes for two or three weeks, taking some musical gear up there, knocking ideas about, taking the Dictaphone with me,” says Bryan.

“Then I had to cultivate a new writing relationship with Olivia, working out how to get the best out of her writing and singing, and it turned out to be refreshing working with her.”

For Olivia, it was a case of “adapting to working with someone else”. “Obviously I’d worked with Bryan for five years on backing vocals and on the Josh & Co tour, but I hadn’t written with him before, so the beauty of it was trying different things, different harmonies,” she says.

In concert, Olivia’s personality is coming to the fore too. “Like every singer, you’re influenced by different people, so I’ve brought a different stage presence from Heather. She had a phenomenal presence in her own right, just I have brought my own thing,” she says.

Celtic music and Pink Floyd carry weight in Mostly Autumn’s music, but Olivia draws on other influences. “It’s more the classic rock of the Seventies and Eighties, which I was ‘forced’ to listen to as a child as my dad [the late York musician Howard Sparnenn] used to play it all the time,” she says. “But there are also artists like David Gates and Bread and Eva Cassidy that have influenced me.”

The Grand Opera House awaits next Saturday. “I can’t wait. I’m really looking forward to it,” says Olivia. “Doing this show with this line-up, with this material, and knowing it’s going to be a big show, it’ll be a great one to do.”

Bryan is eager too: “Sometimes the Opera House has been the beginning of our tours and we’re not necessarily match fit, but this will be a dozen dates in, so we definitely will be.”

Mostly Autumn play Grand Opera House, York, next Saturday, 7.30pm; tickets cost £21 on 0844 847 2322. Go Well Diamond Heart is available in a limited-edition print of 2,500 copies as a double album online at mostlyautumnrecords.com or as a single album.