In 1945 Benjamin Britten heard that Yehudi Menuhin was planning to tour Germany to play to survivors of the concentration camps. The composer begged the violinist to take him too, as accompanist. Both musicians later noted that the horrors they saw during their tour, which including an overnight stay at what was left of Belsen, affected them for the rest of their lives.

Soon afterwards, Britten found a way to channel some of his responses into the final movement of his String Quartet No.2, subtitled Chacony. It was commissioned as a tribute to Purcell on that composer’s 200th anniversary, and modelled on the Chacony by Purcell himself, but the music’s intensity suggests that the formal, structured outline provided an ideal container for the composer’s turbulent emotions.

The choreographer Richard Alston has now created a ballet, Chacony, based on the Purcell and Britten together. His company gives its London premiere at Sadler’s Wells next week as the centrepiece of a triple bill.

Alston is the most musical of contemporary dance-makers and has often been inspired by Britten in the past. But how can anyone turn a response to such horrors into a ballet?

There was never any question, Alston says, of an overt representation of a concentration camp. “I have seen at least two ballets that were about concentration camps, which I frankly found offensive,” he explains. “I didn’t want to trivialise it. Every person on the earth has genuine emotions, which can include a sense of appalling horror when you read about what happened in those camps, but you can’t suddenly pretend that you can create on stage what that looked like. So for me this was a huge question: how could I deal with this music and be true to what was in it?”

His solution is to show the dancers as vulnerable individuals, closely supporting one another. “There is something very dark in the music that I wanted to get to grips with and express, but that should not be about obvious grief-stricken images, but about people being very tender with each other. I can only imagine, but do imagine, that when you have possibly lost several members of your family, if there’s someone close to you who’s still alive then they become that much more important to you. So that’s what I’ve been trying to make clear.”

The legacy of the camps is close to home for one of Alston’s dancers, Nicholas Bodych, who is English on his mother’s side and Polish on his father’s. “My grandparents walked all the way to Rochdale from southern Poland to escape the war,” he recounts. Recently Bodych has travelled through Poland, seeking his roots. He found some — in a list of prisoners-of-war held at Auschwitz. “Bodych is an unusual name and it was quite a shock to see it there in black and white,” he says. Now, he says, he hopes that some of that connection will feed into his performances of Chacony.

In the ballet, the Britten follows the Purcell, in which the dancers are confident, assured individuals, clad in magnificent red. After this, Alston seems to suggest, something terrible has come into their existence and overturned it. Watching, the emotional impact is extraordinary. There’s a gentleness to the dancers’ gestures, while their faces show numbness, shock, humility. They reach out to one another, palms upturned; they support prostrate colleagues; they protect and sometimes almost hide one another.

Vulnerability, rawness and deep humanity are present — yet this ballet is almost abstract. It is as if Alston has extracted from Britten’s musical response the very essence of his emotion and crystallised it. In the end, it is not about concentration camps. It’s about compassion.

Chacony is on at Sadlers Wells June 16 and 17.