After a week in which pop protest involved nothing more dangerous than playing to a vast TV audience, it's worth remembering earlier musical campaigners who faced the threat of arrest or attack for what they were doing.

These days, Sweet Honey in the Rock are the best known black women's a cappella group in the US, but their roots are in the violent civil rights confrontations of the 1960s, when their founder Bernice Johnson Reagon was leader of the Freedom Singers. She was both a campaigner and a powerful gospel singer, and in the 32 years since the group was founded, Sweet Honey have continued that tradition.

This was their first London appearance since Reagon's retirement last year, but the new six-strong line-up (which still included such magnificent veterans as Ysaye Marie Barnwell) continued her policy of social comment, discussing anything from the G8 to murders and domestic violence. That may sound heavy going, just as the presence on stage of two sign-language exponents (one using the American system, one the British) may seem too worthy, but this is a group who manage to be both thoughtful and good fun. These women are disarmingly fine and theatrical entertainers, and after just three songs they had achieved the impossible by getting a London audience to sing in rousing four-part harmony on an African chant.

Then they were off, their voices backed by nothing more than occasional percussion, constantly swapping lead vocals and switching from upbeat gospel and soul to R&B, a delicate jazz-tinged treatment of the old spiritual Motherless Child, or an unexpectedly urgent treatment of Bob Marley's Redemption Song. The sound could have been better (the little radio mics allowed them to dance but didn't do full justice to their fine harmony singing) but even without Reagon, Sweet Honey sounded brave and enthusiastic as ever.