I played Chopin as they sent my family to their deaths

At the age of 106, the concert pianist Alice Sommer Herz is an international celebrity. But despite playing in front of audiences all over the world, perhaps what is most remarkable about her life is her continued capacity for hope in the face of unimaginable suffering.

In 1943, with her husband and their six-year-old son, she was deported from Prague to the Nazis' "model" concentration camp at Terezin; her music helped to sustain her spirit there and throughout her astonishing life.

She has told her tale to film-maker Christopher Nupen, whose tender portrait of her, Everything is a Present, has just been released on DVD; it adds to a catalogue of fascination with Sommer Herz's life that includes the book A Garden of Eden in Hell by Melissa Müller and Reinhard Piechocki, and Nupen's earlier film We Want the Light.

Though frail, she lives independently in a one-room flat in Belsize Park, north London, where she practises the piano for two hours every morning. Although she no longer goes swimming - she did so every day until she was 97 - her memories and her spirit are as vital as ever.

She was born in 1903 in Prague, while the Czech composer Dvorák was still alive. "He is one of the great geniuses of music," she says. "Because of Dvorák, the Czech people will live for hundreds, thousands, of years!"

The Prague of her childhood, she recalls, was a melting pot shared by Czechs, Germans and a large Jewish population. Her family was "Jewish without religion", assimilated and proud to embrace German literature and music as their own heritage.

She was one of five siblings, including a twin sister. Her father ran a factory that made scales (the balancing kind, as opposed to musical ones). He would come home exhausted and fall asleep by 8pm. "Then our mother would say: 'Children, go and play'. She meant 'play music'. My brother was a very fine violinist and we played together from when I was five years old. I still know by heart the pieces we learned then."

Her mother was her musical guide and her "strongest critic"; she always trusted that "if my mother said something was good, it really was". Having been a childhood friend of Mahler, her mother took little Alice to the premiere of Mahler's Second Symphony. Franz Kafka was a family friend too.

Aged 16, Sommer Herz went to play for the great Austrian pianist Artur Schnabel. "I wanted to know what he would say about my playing. But he was not a nice person. He was very money-minded." She pulls a face. "Money is useful, but you should not live for it."

She is very clear about what you should live for. "There are three things in my life," she says. "The love from the mother to the child, which is the basis of everything; nature, which is so beautiful; and music. This is my religion."

She well remembers the misery of the First World War, but despite having experienced that, then later Terezin and the death of her husband, and in 2001 that of her son, she has never become embittered. Quite the opposite - optimism has become her way of life and she is certain that it has contributed to her longevity.

Does she think that difficult experiences early in life make one more resilient? "It enriches you," she suggests.

Sommer Herz's positive nature was seriously challenged when her mother was deported and killed by the Nazis in 1942. Yet while she was devastated, an inner urging prompted her to turn to her music. She threw herself into learning the Chopin Etudes, some of the most technically challenging piano compositions in the repertoire.

But a year later came her own deportation to Terezin. Upstairs in their apartment block lived a Nazi, who used to enjoy hearing her play the piano. While other neighbours made their selection of the Sommers' furniture and effects, he came downstairs to bid them farewell and to express hope that they would return. "He was the most human of our neighbours," she says.

In Terezin, despite appalling conditions, she was determined to live for her son and for her music. In the camp, music became part of daily life. She gave more than 100 concerts there. Many of her fellow inmates were artists, musicians and writers, but there was nothing remotely philanthropic about the Nazis' encouragement of the arts in Terezin. "It was propaganda," she says contemptuously. "This was something they could show the world, while in reality they were killing us."

Her husband was taken away to Auschwitz and later Dachau, where he died of typhus six weeks before the end of the war. His parting words to her were: "Do nothing voluntarily." She believes this saved her life and their son Raphael; other women, offered the chance to follow their husbands, were sent to their deaths. Raphael (whose name was originally Stephan) was one of only 130 children who survived Terezin, out of a total of 15,000 victims. After the war, mother and son moved to Israel, where he grew up to be a much-admired solo cellist. His death during a concert tour in 2001, aged 65, shocked the music world and must have been the greatest grief imaginable for his mother. "Still, I am grateful to have had such a son," she declares. His portrait has pride of place on her wall.

"I have never hated, and I will never hate," she adds. Hitler she regarded as "a madman". She has never made a distinction between German music and any other and regards Wagner as "one of the greatest musical geniuses in history". Her favourite composer? "Beethoven!" she says, laughing, as if it should be obvious.

'Everything is a Present' is released by Allegro Films