It takes balls to play a castrato

The castrato Farinelli was a vocal superstar of the baroque era. Pity, then, today's poor countertenor, forever overshadowed by the mythic magnificence of the castrati who provide most of his repertoire. And whereas the castrati's name proudly boasts of the sacrifice they made to achieve their vocal splendour, the countertenor is a mere falsettist, the very word carrying a sneer of disdain.

The castrato Farinelli was a vocal superstar of the baroque era. Pity, then, today's poor countertenor, forever overshadowed by the mythic magnificence of the castrati who provide most of his repertoire. And whereas the castrati's name proudly boasts of the sacrifice they made to achieve their vocal splendour, the countertenor is a mere falsettist, the very word carrying a sneer of disdain.

It takes balls, then, for Nicholas Clapton to incarnate Farinelli in One God, One Farinelli, "freely translated and adapted" by Clapton himself from Quel delizioso orrore! by Guido Barbieri and Sandro Cappelletto. In this version, we get two Farinellis: the old singer, reminiscing fondly and acerbically about his younger self, whose voice Clapton brings to life. The first sound we hear from the decaying Farinelli, played by Richard O'Brien in Victor Meldrew mode, is not a mellifluous soprano roulade, but a mightily relieved fart.

His guts may be rotting but his memory survives intact, and from his villa, where he is drawing up his will, his thoughts wander back to his glory days. He bombards us with would-be withering recollections - of Casanova, of his rival Senesino, of the infant Mozart, and of mad King Philip of Spain, whom he serenaded for years in an attempt to cure his "hypochondria gravis". And every now and then, memory is salved by the sound of his voice in its pomp.

This is a nice conceit. With Clapton behind a ragged gauze, his voice seemed to reach us, precisely, through the mists of time, but sadly the singer was suffering a throat inflamation, and bravely though he battled, he could not negotiate the outrageous flourishes of the arias he sang (by Handel, Hasse, Porpora and Giacomelli). When his older self evoked a trill, the young Farinelli could only manage a tiny wobble, and of the singer's legendary long breaths there was hardly a trace.

Of course, this could be the point: the old man mis-remembering and being caught out when reality intrudes. It was a possibility allowed for by Robert Shaw's staging which, in Claire Lyth's designs, was efficient enough, but O'Brien needs a firmer hand. He seemed less than wholly engaged, his role supplied with insufficient bons mots to support the amount of barbed camp with which he wanted to invest it. Clapton's instrumental support (harpsichord David Wright, Christopher Suckling baroque cello) was more enthusiastic than refined, and on another evening the singer, never less than wholehearted, will give a fuller account of the musical demands that faced Farinelli. There's the seed of a real show here, but on this first night it rather went off at half-cock.

BAC's Opera 2000 Festival continues until Saturday (020-7223 2223)