AfroReggae are a Brazilian phenomenon. Suddenly famous over here because they opened for the Rolling Stones at last month's free concert on Rio's Copacabana Beach, they are best known back home not just for their music but for the work they have done trying to stop violence in the favelas where they started out.

They aim to show that hip-hop can be a positive force while still providing great dance music, and their opening songs succeeded on both levels. At the front of the stage were three percussionists, bashing away at hefty drums suspended around their waists, while behind them were more drummers, guitar, bass and decks, along with a trio of rappers, performing in front of a large screen showing images of the police brutality that inspired the band to offer an alternative to ghetto confrontation.

It was a stirring start that appeared to justify their inclusion in the Barbican's Tropicalia season. After all, the Tropicalia artists of the 1960s upset the then Brazilian military government with their musical experiments. After an impressive first half hour, the band calmed down. They moved off into unremarkable soul ballads, pop reggae or a dash of reggaeton (a mixture of Jamaican dancehall and Latin hip hop), and the slick staging was often more interesting than the songs.

It took the arrival of the UK duo Estelle and Ty to enthuse the audience for the finale, which included a Brazilian treatment of Lennon's Imagine. By now, uniformed Brazilian police had appeared on stage to stress ghetto unity, and the band were urging tourists to visit their country using Brazil's national airline.

The Tropicalia artists were expelled for their views, but the now-democratic Brazil must be delighted that AfroReggae are such unexpected ambassadors.