Choir of Hard Knocks leaves the streets to sing for supper at Sydney Opera House

Slumped silently on Melbourne's street corners, they had always experienced abuse, never adulation.

And the bizarre notion they might soon be singing to packed audiences at Sydney Opera House would have been treated with derision. But for a group of homeless people that seemingly preposterous scenario is about to come true.

Tonight the appropriately named Choir of Hard Knocks will play the first of three sell-out concerts at the harbour city's most prestigious venue. Cult status has already been achieved, following a hit Australian TV series and similar gigs in Melbourne. Their CD has gone gold and topped the classical charts.

The choir is the brainchild of Jonathon Welch, a renowned opera tenor who believes passionately in the power of music to help deliver social justice, giving the disadvantaged a long overdue voice. Inspired by a similar group of singers in Canada, he followed food vans in Melbourne, telling patrons of his grand plans.

The response was overwhelming and within days more than 50 colourful characters cast out by mainstream society were straining their vocal chords in a far more productive manner.

Singing out of tune was the least of the challenges facing Mr Welch, a former principal at Opera Australia. He also had to contend with problems of addiction, behaviour and personal hygiene. A 'zero aggro' policy was introduced.