As the first performer and dedicatee of Beethoven's Kreutzer sonata, the British violinist George Bridgetower's niche in musical history is secure. But the fact that Bridgetower was black, the son of a Polish mother and possibly a Barbadian former slave, makes him a hugely potent subject for our diverse times. All credit to the City of London, therefore, for commissioning this Bridgetower opera for this year's City of London Festival, to be followed by an autumn UK tour by English Touring Opera.

Billed as a jazz opera, with a score by Julian Joseph and libretto by Mike Phillips, Bridgetower promises much but delivers only intermittently. The piece is certainly ambitious, but Joseph's attempt at a two-hour musical fusion rarely coheres for long. The score swings when it is at its jazziest and sags, sometimes alarmingly, into a dreary minor-key melancholy when it is at its most operatic. Phillips's libretto tries to weave the violin prodigy's story into a critical commentary on the 200th anniversary of the abolition of the slave trade and ends up trying to say too much.

Overall, this reduces the central character to a cipher. Joseph doesn't help by setting Bridgetower's music too low for Cleveland Watkiss to project it easily. Jonathan Peter Kenny, as the Prince of Wales and William Wilberforce, and Buddug Verona James as Lady Holland and Mrs FitzHerbert, make what they can of the more operatically conceived parts of the score. Franz Hepburn is assured as Bridgetower's father and Jamal Hope is touching as the boy violinist.

Easily the best moments come when the remarkable Jacqui Dankworth, as the former slave Mary Prince, is allowed to show off her vocal range and technique with the 10-piece Julian Joseph Big Band at full pelt. Don't go to Bridgetower expecting Beethoven. But there is an effective jazz-song suite trapped inside this honourable failure.

· Touring in the autumn. Details: www.englishtouring opera.org.uk