Pierre Boulez has conducted all the Mahler symphonies at one time or another, but he has made no secret of the fact that the ones that interest him most are the fifth, sixth and seventh - the trilogy of instrumental works that clinched the composer's symphonic mastery. As far as Boulez's concerts in London have been concerned, however, it seems to be the seventh that he has conducted here more regularly than the others in that select group. It was this one that Boulez chose to include in his series of concerts with the London Symphony Orchestra.

Perhaps Boulez - like Schoenberg, who so admired one of the earliest performances that he became an overnight convert to Mahler's cause - admires the radicalism of No 7, the way in which its central trio of movements especially seem to be on the threshold of unexplored musical territory. He does admit that the episodic last movement is problematic, although, as he wrote in the programme for this concert: "I place responsibility for that on my own shoulders, not on Mahler's."

Boulez's solution was to confront the problems head-on, carefully delineating the finale's bombastic paragraphs and making no attempt to impose some spurious continuity upon them. The result was just as vivid as everything in the preceding four movements - the sweep and command of the opening, the deceptive charm of the two Night Music movements, and the spectral imagery of the Scherzo. The orchestral playing was faultless.

The symphony was preceded by the 2003 version of Boulez's own Dérive 2, part of a family of pieces evolved from the raw material of his 1980s electro-acoustic work, Répons. Sustained and sinewy, it is stitched together from the multiplications of a six-note collection of pitches, which rotate around each other in ever-changing combinations. Gradually, the textures get sparer and the sound masses start to aggregate, before the piece stutters out in a sequence of held chords. Always fascinating, if a bit over-extended.