Momentum!/ Mark-Anthony Turnage, Barbican Hall, London <br></br>Academy of Ancient Music, St John's Smith Square, London

Every January, the BBC invades the Barbican for a weekend dedicated to a single composer. This year, under the title Momentum!, it focused on Mark-Anthony Turnage, at 42 the youngest composer ever featured in the series. In six concerts over three days, the assiduous Turnageite could take in seven hours of his music; the truly dedicated could consume even more by attending the "fringe" events at the Guildhall School. Those unconvinced might ask, "Aren't you rather young for a career retrospective?"

But few composers of Turnage's age have such a varied worklist: three operas already (and at least two aborted), symphonic works on the largest scale, miniatures of the utmost delicacy, brash jazz-inspired concertos, doleful song-cycles and more besides.

There were no fewer than five world premieres on offer. Even if two were "revised versions" of works already heard, there were occasional hints that the workload led to mere note-spinning. But there was real vigour in Slide Stride, premiered by the Nash Ensemble. Paying homage to, but never merely imitating the stride piano tradition of 1920's jazz, this often riotous piano quintet had energy to burn. Earlier in the same concert, Ian Brown played True Life Stories, an eloquent and touching suite that, surprisingly, is Turnage's only solo piano piece.

The programming brought context by including music by composers whose work Turnage himself treasures. For the final concert, Leonard Slatkin conducted the BBC Symphony Orchestra and Chorus in Stravinsky's Symphony of Psalms. To follow, the world premiere of Turnage's The Game is Over, clearly a companion piece. Like Stravinsky, Turnage gives the wind section precedence over strings, and his setting of Ingeborg Bachman's poetry (in translation) shared the hieratic atmosphere that suffuses the Symphony of Psalms. A quasi-operatic soprano solo seemed merely conventional when the choral writing provided all the drama needed, while plaintive flugelhorn moans from the back of the auditorium emphasised the poignancy of the closing words, "Dearest brother, my brother".

Turnage has paid homage in several works to the memory of his younger brother, Andy, who died from drug addiction in 1993. I don't know whether Andy is the "brother" referred to in The Game is Over, but the references are explicit in the titles of several movements of Blood on the Floor: "Junior Addict", "Needles", "Elegy for Andy". A concerto for amplified jazz trio and orchestra, Blood on the Floor opened the Turnage weekend in a BBC Symphony Orchestra performance conducted by Martyn Brabbins. The work's impact has not diminished since its 1996 premiere, even if the amplification here sometimes obliterated inner details.

This was the first Turnage piece written specifically for jazz players, allowing a space in the dense orchestration for drums (Pete Erskine), amplified sax (Martin Robertson) and electric guitar (John Parricelli). He does more than write them into the piece: he gives them room to improvise through certain passages, a bold move when most contemporary composers consider improvisation an alien import that threatens their craft.

Not so Turnage, whose enthusiasm for jazz matches his love of classical music. Blood on the Floor is his most thoroughgoing attempt to integrate jazz colours and procedures. He followed it five years later with Bass Inventions, written for jazz bassist Dave Holland and the Birmingham Contemporary Music Group. Under Alexander Briger, the same forces performed the piece on Sunday, but while there is plenty to admire, the suspicion remains that Turnage loves Holland's cantabile bass so much that he grants it rather too much space.

It implies no lack of enthusiasm for Turnage's recent work to say that the most powerful piece heard during Momentum! was one of his earliest. Greek, his first opera, had its premiere in 1988, when its truculent humour and raucous effing and blinding seemed entirely a response to Thatcherism. Fifteen years on, the anger has not diminished, yet the opera, released from a particular historical moment, now emerges as a wholly original work.

It's as if, not yet knowing that modern opera is problematic, the young Turnage simply fashioned his own rules, mixing agitprop and melodrama, Singspiel and lyric opera according to the demands of the moment. Of course, Steven Berkoff deserves some of the credit for writing the play that generated the opera; similarly, Turnage benefited from Jonathan Moore's collaboration on the libretto. But the end-product is echt-Turnage.

Jac van Steen coaxed a convincingly wholehearted performance from the London Sinfonietta and a cast dominated by Roderick Williams as Eddy, the Oedipal wide-boy at the opera's epicentre. Clare Venables provided a staging that, in its emblematic, cartoon-like simplicity, had all the boldness the work required. It's a shame that too little of the text was audible. Amplification was occasionally in evidence: perhaps it should have been used throughout. Yet this was an uplifting performance. Has any British composer written a better opera since Greek? Not that I've heard, and not even Turnage himself, who has since learnt how difficult opera is.

Period instrument modes and manners ruled at last Tuesday's Academy of Ancient Music chamber concert as fortepianist Robert Levin joined four of the orchestra's wind-players in Mozart and Beethoven. At first the instruments sounded as if they had been subjected to whatever the opposite of amplification might be, but once the ear adjusted the instruments' salty tang exerted its familiar appeal. Yet in Mozart's K452 Wind Quintet, Levin's lead was too deliberate, some of the notes emanating from the wind instruments were too wild for comfort, and at times the attenuated rhythm threatened to stop the music in its tracks.

The muted rhetorical flourish that opens Beethoven's Pathétique sonata suited Levin's fortepiano much better. As the tempo increased and the mood became more agitated, it was almost possible to hear the instrument's fragile innards complaining at Levin's pounding, creating an entirely appropriate sense of titanic struggle. Levin's freely shaped performance might even have convinced sceptics of the fortepiano's merits.

After the interval, a marvellously energised and energising performance of Beethoven's Opus 16 Wind Quintet showed no trace of the gravid rhythms that had threatened the Mozart. The keyboard's low notes hummed like a gently bowed string instrument, each of the wind players delivered a pungent solo, and the idea that these might be "ancient" instruments seemed preposterous. For the moment, if not forever, this was how the music should sound.

Anna Picard returns next week