In the 1990s the German singer Ute Lemper became a lynchpin of a ground-breaking series of recordings on the Decca label entitled Entartete Musik. It explored composers banned by the Nazis, including much music that had scarcely been heard for decades. Lemper, whose sultry stylishness often seems to channel Marlene Dietrich, set alight the songs of Kurt Weill and Bertolt Brecht, Mischa Spoliansky, Friedrich Hollaender and others for a new generation. Now she is back, exploring even darker territory. On May 22 she brings Songs for Eternity to JW3: a programme of songs written in the ghettos and concentration camps.

“It’s one of my most serious, researched and heart-breaking projects,” says Lemper, who originally developed it for the 70th anniversary of the liberation of Auschwitz in January 2015. It began when she met the musicologist Francesco Latoro; researching songs written between 1942 and 1944 in the concentration camps, he encouraged her to explore them. “Also, I had had a book on my piano for 15 years — Songs Never Silenced,” says Lemper. “It was given to me by an Israeli Mexican promoter: a collection of songs written in the ghettos.”

“Some songs reflect life behind barbed wire or the ghetto walls. Some are very sad, for instance about the assassination of the children in the ghetto. Others are songs of hope, songs of rebellion— even if sometimes the only rebellion lies in hope. One famous song Stille, stille says that rebellion lies in keeping quiet about the hope we have in our hearts.” Most are in Yiddish: “I have a good friend, a rabbi, who taught me the various different accents and heritages of Lithuanian, German and Polish Yiddish.”

One of the most devastating histories is that of Ilse Weber, a writer who set her own poems to music. Transported to Theresienstadt from the Prague ghetto, she became a children’s nurse and eventually went with her young charges to the gas chambers in Auschwitz. “She knew the shower rooms would be the path to death,” says Lemper. “She said to them: ‘Let’s get into the shower rooms, breathe deeply and sing as loudly as we can,’ because she knew that with the deep inhalation of the gas, the agony of dying could be shortened. Until the last moment she wanted to do something good.”

The project is relevant not only to the past: today, Lemper says, we witness “the rise of nationalism and populism, from Brexit to Trump to right-wing parties in Germany, France and Austria.

“People are saying racist things that they should never say, advertising intolerance and reactionary nationalism. Thousands of people have been displaced because they are not born with the privilege of freedom, peace, education and religious freedom. They fear for their lives in the middle of genocide and war — yet these people are often not even let in because of the fear of terrorism. Many thousands of innocent people are rejected, sitting in front of barbed wires or in immigration rooms, or simply being sent back. I feel broken-hearted when I see this, and the way the population rejects the responsibility to take care of others in a world that we have created of unbalanced wealth and education.”

Performing this programme is an emotional challenge: “The first time, my throat clogged up so much that I couldn’t swallow,” she says. “It was almost impossible to be a medium for these stories – and it still is very difficult. But it’s a mission for me to keep this repertoire alive, to never silence it, to remind us of the past. Especially as a post-war German it is most important to me to do this. I feel deeply connected to this music and I’m putting it out there.”

She has long embraced Jewish culture at a deep level: “I’m married to a Jewish man, my children are barmitzvahed and I’ve lived in NY for 20 years,” she says. “My first husband was Jewish too and both of them would say that I am much more Jewish than they are!”

Ute Lemper’s Songs for Eternity is at JW3 on 22 May. Booking: jw3.org.uk/event/ute-lemper#.WuRKVi-ZMQ8