PROMS: Gustav Mahler YO / Pierre Boulez; Orchestra of St John's Smith Square / John Lubbock; Royal Albert Hall, London / Radio 3

Tuesday's early-evening three-quartets-and-a-ballet programme, with which Pierre Boulez and the Gustav Mahler Youth Orchestra had opened the Edinburgh Festival on Sunday (already reviewed from there) played to a packed Albert Hall. And a sweaty one, which can't have made it easy for the instrumentalists of this excellent European youth orchestra. Nicholas Kenyon boldly began the pre-Prom talk by challenging Boulez, scourge of the "regurgitations" of neo-classicism and post-modernism, over his inclusion of Ravel's Le tombeau de Couperin, with its re-creations of 18th-century dance forms.

Was it merely fanciful to think the performance of the Ravel reflected lingering Boulezian doubts? Perhaps. But the whole evening rather moved in and out of focus, and even The Rite of Spring was only a qualified success. It was good to hear the composer's own brilliant Notations I- IV, though. And to learn in the pre-Prom talk that he's working on Nos 5-8 this winter. ("No conducting." But how many times have we heard him play that one?)

A rather smaller crowd assembled for the late-night American show. At the start, this seemed in danger of turning into a rather damp squib after Stravinsky's fireworks. Newly converted enthusiast for Lou Harrison that I am, after the cliche-busting Organ Concerto earlier in the season, I have to admit that his New First Suite for Strings is tame stuff: oddly English in a rather wan, neo-baroque sort of way, at least until the cellos and basses suddenly decide to provide some percussive accompaniment on the bodies of their instruments.

I was there when the late lamented Yvar Mikhashoff premiered Stephen Montague's Piano Concerto at the 1988 Almeida Festival, and can confirm that the composer's subsequent decision to "take the work out behind the barn and shoot it" was the kindest thing in the circumstances. Its replacement is a much more substantial affair, though all Montague's characteristically entertaining manners and mannerisms are still there: notably the fast repeated notes and perambulating clusters in the piano part. Rolf Hind, the indefatigable soloist, had to stand up to dispatch the forearm clusters at the end of the first movement.

His new obsession with American vernacular materials could easily turn Montague the Showman into Montague the Manic Preacher or Montague the Pioneer of Ultimate Schmaltz. Hymn tunes and Negro spirituals - notably "Were you there when they crucified my Lord?" - are here, however, expertly and sometimes movingly worked into the mix. The composer's increased experience in writing for orchestra is shown to good effect, to the extent of overshadowing the soloist, which is something of a problem. The use of solo trumpet high up in the hall's gallery is an obvious idea, but Montague's risk in employing it in all three movements pays off, as it is integrated so well into its contexts. Even the honky-tonk transformation of the piano in the second movement - another dangerous device - produces some moments of real poetry.

The Orchestra of St John's, under John Lubbock, was excellent, often emotionally charged. The infamous Barber Adagio was perfect in this setting. And Colin McPhee's Tabuh-tabuhan, with Hind and Thomas Ades as the two pianists, offered subtle blandishments as well as good entertainment at the close of another long evening.

Boulez Prom repeated 2pm Mon on R3 Keith Potter