Into the Little Hill/Down by the Greenwood Side, Royal Opera House, Linbury Theatre, London

Unpredictable stuff, electricity.

While 'Rigoletto' was going full-blast in Covent Garden's main auditorium, events downstairs in the Linbury studio theatre were suddenly brought to a halt by a power-cut. George Benjamin had just begun to conduct the long-awaited London premiere of his chamber opera 'Into the Little Hill' - with two outstanding soloists and the London Sinfonietta in brilliant form - when everything was plunged into blackness. Time passed, people waited, the power stayed off, and at 10.30pm Benjamin and his performers defiantly delivered a concert performance in the foyer.

'Electricity' was one of the words in Martin Crimp's libretto which Benjamin had confessed to being uneasy about setting to music. While the plot follows the medieval Pied Piper, and while Benjamin's imagination is rooted in mythical timelessness, Crimp's thoughts are contemporary and political. Benjamin needn't have worried: 'electricity' comes out sweetly as part of a long musical line – and having returned the next day to hear this 40-minute work in proper conditions, I can report that its meld of words and music is a particularly happy one.

Heroically playing all the parts in this pullulating scenario, soprano Claire Booth and mezzo Susan Bickley make a fine vocal match, greatly helped by the fact that Benjamin's word-setting is as expressive as Debussy's in 'Pelleas et Melisande'. The orchestral writing, meanwhile, responds with delicate precision to Crimp's terse and vivid poetry. Read cold, the libretto raises 'issues' – child-abduction, the politics of immigration – but in performance these are so muted as to be barely perceptible. Every piece of music leaves its own particular silence in its wake: the silence left after this work's last notes sounded was exquisite.

But this was only half of a brilliant double-bill which Opera Group is now taking on national tour: the other part is a revival of Harrison Birtwistle's rumbustious pastorale 'Down by the Greenwood Side', with Claire Booth playing the central character as a bag-lady. If John Fulljames's direction of the Benjamin – abetted by Soutra Gilmour's designs - is a model of refined restraint, his treatment of this semi-spoken parable of murder and miraculous rebirth (to Michael Nyman's libretto) is spirited and wonderfully coarse-grained – which can also be said of the orchestra and actors. Pip Donaghy makes the sleaziest Father Christmas I've ever seen.