Proms BBC SCOTTISH SO; ROYAL LIVERPOOL PHILHARMONIC ORCHESTRA Royal Albert Hall, London / Radio 3

Sibelius, an extravagant drinker, once described the difference between most late-Romantic music and his own as the contrast between cocktails and spring water. Irony apart, this bon mot formed an interesting starting point for last weekend's Proms, featuring his Fifth Symphony on Saturday night and the following evening Mahler's poignant, searching Ninth.

In the event, both works proved intoxicating, but from the unusual position of purity. In the Fifth, this is intrinsic to the music. Played straight, the symphony glides through its web of tensions where keys and thematic events lie in masterful contradiction until all is resolved in the final gesture of abrupt, hammer-swinging chords.

But, conducted by Osmo Vanska, a noted Sibelian (though new to the Proms), the work acquired a heightened drama through lustre added to the pure lines of form. Laced with exaggeration, this account might have ended up as melodrama: background string textures in the first and second movements were pared down to the threshold of hearing, while generous rubatos applied throughout seemed almost ready to pull the music backwards.

Yet, as his clean, persuasive reading of Finlandia had already suggested, Vanska proved too clever to fall victim to his own tricks. Both dynamic and supple in approach, he kept the music alive with expectation.

In Beethoven's Triple Concerto, soloists' problems of intonation removed the shine from an otherwise interesting reading. Conductor Peter Mark took the baton for excerpts from Act 2 of Thea Musgrave's Simn Bolvar, giving us the first hearing of an opera recently premiered in Virginia and co-commissioned by Scottish Opera, though yet to be staged over here.

Epic Verdian opera needs epic musical style, which was the missing element in an otherwise well balanced array of "bleeding chunks". But everything else about this piece sounded exemplary. Musgrave's invention, atmospheric yet mobile, pushed the music forward phrase by arching phrase. Her dark yet delicate scoring betrayed a refined ear. Her sense of theatre, reflected in a love duet between Bolvar (sung by tenor Stephen Guggenheim) and Manuela (soprano Amy Johnson) and an explosive conflict between Bolvar and his general, Santander (baritone Douglas Nagel), boded well for a British production, which is now overdue.

Theatre, in the wide arena of the Albert Hall, proved unavoidable in Libor Pesek's Mahler, with the Royal Liverpool Philharmonic on Sunday in great shape and relishing the chance for solo displays. Horns, the alpha and omega of this piece, never faltered. In the two central movements, lapping waltz and contrapuntal cataclysm, woodwind and brass made worthy contributions. But the work's touchstone is the finale, and the hard-won purity of its closing pages in particular. Pesek kept a steady pace - there's nothing flashy about his presentation - and reached the end with the sense that it had been present from the beginning. Some conductors make the symphony a vehicle for their own personality. Here, it was the composer who counted all the way.