Streetwise Opera has been much praised over the past five years for its transforming work with the homeless, with workshops and staged performances in which professional singers work alongside the amateurs. Here, the company's collaboration with The Shout, a professional choir that has a reputation for celebrating musical diversity in a vividly theatrical way, could have been compelling - but Critical Mass, devised by director Emma Bernard and composer Orlando Gough, is a disappointment, neither dramatically involving nor musically rewarding.

In Bernard's staging, the performers are besuited, briefcase-wielding delegates to an unnamed political party's conference, though they sing The Red Flag so it's obviously not New Labour. Cliches and platitudes about the perennial conference issues of inequality, education, racial integration and the environment are reeled off at the slightest provocation. Against that deadening background, individuals break suddenly into song - cosmopolitan gleanings from the memories of those who attended the Streetwise workshops, and arranged for unaccompanied chorus by Gough.

The point, I think, is to contrast the strength and vivid muscularity of vernacular song with the self-serving impotence of political rhetoric. It is not a very profound observation, nor a rich enough seam to sustain 70 minutes of theatre, and the material needs to be shaped with more dramatic flair than it has been.

For all the hard work and commitment of those involved, there is a lack of slickness and energy about the performance (half the singers are professionals, after all). Earnest intentions and, for the Islington audience, the feelgood sense of supporting a worthwhile cause do not guarantee a worthwhile piece of theatre.