They have the voices of angels if perhaps not the behaviour of heavenly beings. 

However, the actress leads for the new film version of the uplifting smash-hit musical Our Ladies of Perpetual Succour benefitted from a bit of help in the singing department.

The choral performances that are central to the new movie, which is based on the Alan Warner novel The Sopranos, were largely made up of singers from the University of Glasgow's Chapel Choir, who had to soften their received pronunciation to sound more like foul-mouthed teenagers from a Fort William convent school.

Set in 1996, Michael Caton-Jones' raucous rites-of-passage comedy charts the exploits of a group of Catholic schoolgirls in Edinburgh in the adrenalin-packed few hours before their choral competition and stars a cast of relative unknowns led by Tallulah Greive as teenage narrator Orla. 

READ MORE: Hamish Hawk on lockdown and creativity 

Music is central to the movie and it's an eclectic soundtrack, put together by Scottish singer–songwriting duo Roddy Hart and Tommy Reilly. For those who haven't seen the movie yet expect everything from Bruce Springsteen and Burns to Big Country and Motown classics performed by Moray-born Marli Siu in a stand-out Karaoke scene.

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Katy Lavinia Cooper, who leads the University of Glasgow Chapel Choir, also drafted in some of her smaller, close-harmony group, The Madrigirls, for the recording sessions. 

"They wanted a fairly young choir because obviously it's a choir of schoolgirls," says Cooper, who lives in Glasgow's west end.

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"I suggested we used a combination of the Chapel Choir and the Madrigirls. They all sing in a way that wouldn't be age-able.

READ MORE: Our Ladies Review: Raucous and funny take on Alan Warner's novel The Sopranos

"Roddy and Tommy sent me the scores, some of which were part-arranged. I don't want to give myself too much credit, I basically fleshed them out and converted the Bruce Springsteen number for choir and arranged Ae Fond Kiss. 

"Getting the choir together wasn't difficult, it was term time and during the day and there were lots of takes as recording for choirs does take a bit of time."

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She said the director was on hand during the sessions to ensure their performances sounded authentic and subtle voice inflections matched what was happening in the movie.

"We had to make decisions about what accents to use because we quite often sing Scottish songs in Scots with the Madrigirls but with Chapel Choir, you tend to sing in RP. 

"We had to de-Scoticise the way we were singing Burns because we would automatically sing broken-herted nd he was like, no, I think they would sing hearted.

"We had one rehearsal where all the actresses and extras but it was just to sing it through, but they didn't actually have to sing, they just had to look like they were singing the words at the right time.

READ MORE: Tallulah Greive on the film adaptation of Our Ladies of Perpetual Succour 

"It's really well matched,"she added. "Four of us went in quite recently to do some over-dubbing for the bit where one of the girls in the film rushes out during the performance to throw up - we had to sort of pretend to be pushed aside as she walked past."

It's not the first time the Madrigals' beatific harmonies have caught the attention of TV and film moguls. They were enlisted for the soundtrack to the BBC drama - Fiona's Story - starring Gina McKee, who performed with the choir.

"We are very fortunate to get the interesting projects that land on our door," says Cooper.

Emmy award-winning singer songwriter Roddy Hart says Michael Caton-Jones was very specific about the type of music he wanted to make the storylines sing.

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"We knew because we had seen the musical that there was so much scope for different genres of music, because they are in a choir but also have this alternate life outside the choir," he said.

"They visit a karaoke bar in Edinburgh but also Michael Caton-Jones wanted some scored moments, especially towards the end of the film as the drama intensifies.

"Alan Warner is a huge music fan, he's always talking about music in his books and Michael Caton-Jones gave us a Spotify play-list for when we read the script. We knew he had very definite ideas about the type of music he wanted.

"It was a dream project for us as musicians."