Proms 27/28:London Sinfonietta/Atherton, Royal Albert Hall<br/>BBC Philharmonic/Noseda, Royal Albert Hall

London Sinfonietta/Atherton: <img src="http://www.independent.co.uk/multimedia/archive/00231/4-STARS_231323a.gif"></img> BBC Philharmonic/Noseda: <img src="http://www.independent.co.uk/multimedia/archive/00231/3-STARS_231324a.gif"> </img>

"Ideas are ten-a-penny," said Harrison Birtwistle before his late-night 75th-birthday Prom, adding "the problem is their realisation." Hence his delight that the London Sinfonietta, who have loyally premiered his works over the past 40 years, should be officiating once again under their founder-conductor David Atherton. "A gift from heaven, a composite virtuosity" was his comment on their ever-dependable excellence, and the sure-footed way they negotiated the pitfalls of three of his early works amply bore this judgment out.

But the real discovery of this Birtwistle bash was how constant his compositional voice has been: always the same purity of intention, and clarity of execution; always the same obsession with myth, ritual, dance, and multiple perceptions of time. First came "Carmen arcadiae mechanicae perpetuum", a 1977 work composed in homage to the painter Paul Klee and comprising six ‘mechanisms’ which are rotated to form 22 "moments". As David Beard's illuminating programme note observes, the implication is that each such moment is part of a larger event which we never hear in its entirety. The effect was playful and provocative.

Then came "Silbury Air", inspired by what Birtwistle describes as the "hidden formality" he finds in that prehistoric mound in Wiltshire. "There's a strict logic in the piece which I don't want to explain to you" he warned us: as the pulsing, ticking rhythms yielded to woodwind melody, one realised that this defiantly arcane approach was actually appropriate - one could sense the logic, without "knowing" it.

The third piece, "Verses for Ensembles’, was the first of Birtwistle's many attempts to make musical form visible by having his players circumambulate the stage. But shut your eyes - or listen to it on radio - and the whole point was lost.

The programme for Prom 28, given by the BBC Philharmonic under the direction of Gianandrea Noseda, had inbuilt limitations. "Scenes de ballet", which Stravinsky wrote for Broadway in 1944, is a pale and inferior reflection of his earlier neo-classical ballet "Apollo". Even with the nimble Karen Geoghegan as soloist, Mozart's Bassoon Concerto K 191 still came across like an elephant dancing on stilts. And not even Noseda's brilliance could prevent Mahler’s sprawling, self-indulgent, 85-minute Sixth Symphony from seeming - to this non-Mahlerian at least - interminable. But the cow-bells rang prettily from the recesses of the dome.