On 23 August, 1976, a 13-year-old violinist made her debut at the Lucerne festival – with her older brother Christoph at the piano. By the time the concert finished Anne-Sophie Mutter was the toast of the festival, invited to play for no less than Herbert von Karajan. It was the start of a career that has since yielded more than 50 albums, four Grammy awards, and works by a Who’s Who of 20th-century greats: Krzysztof Penderecki; Henri Dutilleux; Witold Lutosławski; Sofia Gubaidulina; John Williams.

So now, aged 62, Mutter is celebrating 50 years on the concert platform. And she’s doing it her way. If anyone was expecting the German star to launch her anniversary tour on Saturday night with a big concerto, they will have been disappointed. An only somewhat full Barbican Hall suggested fans may have voted with their feet. Those who risked it got Mutter in activist mode, using her platform not to revisit triumphs but to champion new music and young artists.

Both were represented in Aftab Darvishi’s Likoo – a lament for solo violin whose drooping phrase-ends and vibratoless opening song mourn the women silenced, imprisoned and killed by the Iranian regime. Grief turns to anger, rhapsodic and insistent, before dropping to a whisper in music that claims the violin’s traditional virtuoso gestures (Bach’s ghost is here, Paganini too) for intimate, confessional expression.

It is a ravishing piece, but its clarity of voice and the emotional weight packed into its small frame sat awkwardly between two occasional pieces by Mutter’s sometime husband and longtime collaborator André Previn. Both the piano-violin duo The Fifth Season (a companion to Vivaldi – weather changeable) and his brittle, jazz-inflected Piano Trio No 1 are the products of, as Mutter put it, “a man without a home”: musical magpies, alighting everywhere and settling nowhere.

Mutter’s brilliance and generosity of tone, her incisive delivery, make an event out of anything she plays, but it was a relief after the interval to have Beethoven doing the heavy lifting. His final “Archduke” Trio gave Mutter, cellist Maximilian Hornung and pianist Lauma Skride a chance for more sustained interplay. Keenly musical and responsive, it was a joyful collective utterance: a statement of intent from a soloist more interested in the music than the limelight.