MUSIC / Skating over the depths: Nick Kimberley on the King's Singers at the Barbican, London

It isn't often that a work by the Hungarian composer Gyorgy Ligeti receives a warm welcome from a full house at the Barbican, London, but it happened at last Saturday's 25th anniversary concert by the King's Singers. So ardent are the fans that the a cappella sextet would get an ovation for singing its way through the alphabet. Which is exactly what it did in the second of three 'Nonsense Madrigals' by Ligeti.

Nor were the Ligeti pieces mere tokens selected at random from the contemporary repertoire. The songs form part of a longer cycle commissioned by the King's Singers, whose vocal expertise must be a valuable asset to composers looking for techniques to extend creative possibility. The King's Singers embody vocal perfection, each voice faultlessly pitched and offering support to every other voice.

That perfection is, of course, central to the group's popularity, but where the perfection of, say, Luciano Pavarotti or Jessye Norman offers a glimpse of the unattainable, the King's Singers seem to offer a kind of democratic perfection. No voice stands out, all contribute to the sodality. It's the kind of perfection we dream of when we sing in the bath: sonorous, well upholstered, apparently effortless. That is not a wholly negative judgement, and certainly the rapturous standing ovation which greeted the encores does rather circumvent criticism. This 25th anniversary concert felt like a fans' convention. The excursion coaches lined the block, and a group member proudly listed all the parts of the world from which people had come to be here tonight. The occasion had added poignancy in that the foundermembers Alastair Hume and Simon Carrington were giving farewell performances. Such occasions demand critical tolerance, and it would be hard to fault the vocal precision, as apparent in Ligeti as in Monteverdi, or in their own arrangement of a Billy Joel song (the second half consisted of arrangements of popular songs, from Gershwin to Paul Simon and - naturally - the Beatles).

Yet there's a sense in which that vocal precision draws a veil over vocal passion. When the popular songs demanded a solo part, each voice sounded strangely colourless, as if unable to let loose outside the supportive framework of close harmony. The technique is so secure, but the art of popular song is knowing the point at which technique no longer helps but hinders. The one moment at which precision and passion married was in a set of songs by the group member Bob Chilcott, performed with the Girl Choristers of Salisbury cathedral.

There were several wry comments from the stage about a piece that had appeared in the European, denouncing the King's Singers as 'mostly middle-aged men in suits'. The problem, it seems to me, is not the suits nor the middle-age. It is middle-class. Brilliantly accomplished, effortlessly social, the King's Singers impress while skating over the emotional depths. That is very comfortable, very English, and very middle-class.