MUSIC / Where the past meets the future: Premieres of 19th-century opera and 50 years of contemporary music in London

London this week has been overflowing with opera: old, new-old, revived and restored. At the Coliseum, Jonathan Miller's Mikado entered its sixth glorious season. In the City itself, Donizetti's The Siege of Calais, much admired yet never before staged in Britain, was premiered by the enterprising Guildhall Opera School. And at the Queen Elizabeth Hall on Saturday night, admirers of Verdi's Stiffelio had a chance to hear a 19th-century equivalent of the Director's Cut: the composer's reworking of the earlier opera into Aroldo, turning the story of a cuckolded 19th-century pastor into the improbable tale of a cuckolded medieval crusader.

Stephen Medcalf's no-frills attitude to the Donizetti offered the best possible approach to a little-known piece. There are fine heroic roles here - for the Mayor of Calais, for his son, Aurelio (a travesti part), and Margaret, Queen of England. An avoidance of the traditional aria sequence gives the work a particularly strong thrust, reinforced by reminiscence motifs (stealthy pizzicatos for the English). Only the third-act ballet (English army defeating the Scottish) was a disappointment, badly performed and dramatically superfluous.

Scotland also fares rather badly in Act 4 of Aroldo. This is an opera that leads from first to last through its musical strength, and this concert performance by the Chelsea Opera group, under Sir Edward Downes, showed that in opera music comes first. There was fine orchestral playing, with pockets of curious ensembles - cello, cor anglais and voice at one point, and a sparsely orchestrated storm interlude - within the overall tutti; also some inspired choral singing. But the laurels went to baritone Anthony Michaels-Moore, distressed knightly father of the heroine. The thrilling, stentorian tones of his Act 3 revenge aria earned spontaneous applause. This was a fascinating introduction to a new world.

Introductions of a different kind were made at the SPNM anniversary week, celebrating 50 years of support for new music with a variety of events, culminating in a QEH gala concert on Sunday afternoon. Caveats surfaced, as well as plaudits. Michael Gorodecki, putting the composer's view, stressed the boon of practical knowledge gained from the society's workshop events. The urge to throw everything into a single piece was one problem he candidly identified, an urge that not all his confreres had mastered, to judge by Sunday's recital.

On Saturday, composers and youth orchestras from around the country assembled in Christchurch Spitalfields for an afternoon of string music. Framed by Philip Cashian's glowing Birthday Chorale, this was a performers' event. But the audience, too, must have caught the boundless energy - early Tippett meets minimalism - in Kevin Malone's Suspicious Motives, and the more lustrous tones of Colin Riley's Evocation, played by the City of Leeds Youth Orchestra. Sadie Harrison's Hoploits and Anthems, and Karen Markham's In Search of Queen Mab made more than just a token showing for women composers.

Markham's energetic Whirligig, performed by Jane's Minstrels, featured at the QEH on Sunday. With Anthony Gilbert's Love Poems - long, glowingly expressive ariosos, sparse, pointed accompaniments - this was the most attractive work of the afternoon. Birtwistle's Cantata and Diana Burrell's Barrow offered sterner stuff. There were interesting donnes - too many - in Tom Ingoldsby's Te Rerioa and Yannis Kyriakides' No One's Filming. As yet undiscovered was the intuitive knowledge of how long a piece of music should be. As Gorodecki suggests, composition is the search for a musical essence conducted through choices of omission: an essence that, in C Day Lewis's words, 'shall spring / From the not saying everything'.