London Philharmonic/Harding, Royal Festival Hall, London

Performances of Mahler's massive 10th Symphony are not frequent. Mahler began writing it in 1910 but left it far from finished at his death a year later. In 1924, his widow, Alma, invited Ernst Krenek to advise on whether the work could be completed and, with the help of Alban Berg, performing versions were made of two movements. More of the work came to light: a continuous score on four or five staves with indications of orchestration as well as orchestral drafts emerged.

In 1960, Deryck Cooke prepared an almost complete performing version, going on to make a complete performing score. But Bruno Walter was against it. "The unfinished work of a musical genius should not be touched".

Fortunately, Walter's advice was not followed. Cooke made further "improvements" with the help of Colin and David Matthews and a definitive score was published in 1976. Although we will never know what Mahler's final intentions may have been - and, indeed, others have made alternative attempts at "reconstruction" - this edition, as performed by the London Philharmonic under Daniel Harding, is wholly remarkable.

Mahler's 10th is about as autobiographical as a work can get. He knew he was dying and that his marriage was falling apart. The symphony is notionally in a horrifyingly difficult key - F sharp major - with a score littered with accidentals including double sharps. Moments of relaxation are rare while moments of exposure are dangerously frequent. The violas' long opening theme, deathly in its chromaticism, weaves a bleak meandering trail.

In this performance unisons were often approximate but with this key and these kinds of elephant traps, pity is probably appropriate. In this movement, the nine-note "scream" - the aural equivalent of Münch - came over as deliberately placed, Daniel Harding not yet confident in his pacing. In the following two movements, Harding set tempi that were too fast for comfort. This led to extreme edginess, a brittle harshness of sound - at times appropriate - but also accident prone. The orchestra seemed unsettled, and it was not until the final movement, with its premonitions of Death portrayed by the thud of bass drum, that Harding allowed the score to breathe. The most beautiful music-making came from the principal flute.

Mahler's symphony was prefaced by a insecure performance of Britten's Serenade for tenor, horn and strings. Ian Bostridge seemed uneasy, his first entry fierce and with overly full vibrato. Best was his bitingly ironic delivery of the Dirge, although why he appeared so reluctant to address us rather than singing into his chest, was a mystery. Richard Bissill, the horn soloist, producedmarvellously raw sounds in a careful performance.