They have been performing publicly now for 20 years, but it wasn’t until their haunting cover of Radiohead’s Creep was used on the trailer for 2010 Hollywood blockbuster The Social Network that indie rock choir Scala & Kolacny Brothers achieved worldwide acclaim.

It’s a firm fixture on the Belgian all-women choir’s setlist, so expect to hear it at the group’s one-off UK 20th anniversary show at the Union Chapel on Tuesday.

“Everywhere we go, people recognise it, they know it from the movie,” says Steven Kolacny, who arranges, and accompanies the choir on piano, while the other Kolacny brother, Stijn, conducts.

“We still love playing Creep on stage. We cannot escape the song.”

The track is a typical Scala cover version – a tightly arranged harmonic chorus of other-worldly female voices singing a well-loved rock song, most often originally sung by a man. Their other hits include covers of U2’s With or Without You, as featured on ITV’s Downtown Abbey, and Every Breath You Take by The Police.

Steven says there’s no formula for choosing a song to cover, but that indie songs with dark themes seem to work best.

Explaining how he chose Creep, he adds: “It all started with a bootleg I had from XFM. It was Thom Yorke playing Creep with Jonny Greenwood acoustically, just with an acoustic guitar and his voice.

“I am a Radiohead fan so I was deeply impressed by it and I was wondering why there were no choirs doing things like that.

“It was easy to change the guitar into the piano and to replace Thom Yorke’s voice with the girls. The results were amazing, it was so overwhelming.”

Scala started in the Kolacny Brothers’ home city of Aarschot in 1996. After a semi-successful career as classical concert pianists, the brothers were looking for a new project: something fun, with no stress, far removed from the classical world.

After spending so long performing solo, the idea of forming a choir appealed to both, and the pair held auditions.

For the first two years, the choir was a mixed group of amateur teenage boys and girls.

But the ethereal quality of the girls’ voices quickly made the brothers determined to make Scala women only and one by one, the boys left. Now, it is a group of professional female singers, all aged about 25.

“The sound of the girls was so touching. If you let them sing something really emotional, it’s a completely different thing than when it’s done by boys,” says Steven.

“It’s hard to explain but if you hear songs by Scala, like With or Without You, or Creep, if it was done by a boys choir, it would be really awful.

“No-one expects those songs to be sung by girls, and that’s what Scala was looking for.”

In their 20th year, the group is celebrating the anniversary with a run of 11 shows in their home city, a string of European dates, and the upcoming show in Islington - the first in the UK since 2011, which was also at the Union Chapel.

The anniversary has made the brothers reflect on their proudest achievements.

“The first time you go to a big city or foreign country, you never forget,” says Steven. “The first time in America, the first time in the UK... the first time is always the best because the city is impressive. You were never there before, and you will never forget it.”

Doors open on April 26 at the Union Chapel at 7pm. Tickets £22.50, booking information: unionchapel.org.uk.