There must be more conductors of international class per capita in Finland than anywhere else in the world. But even by that country's standards Mikko Franck is remarkable. Just 22, he has already taken charge of a host of orchestras, including the Berlin Philharmonic, and has an operatic repertoire of which many conductors twice his age would be proud. Last year he appeared at the Royal Festival Hall with the Philharmonia; on Thursday he made his debut with the London Symphony Orchestra.

Franck's first disc, superbly visceral and thrilling, was of music by Sibelius, which for a Finn goes with the territory. His programme at the Barbican was all Mahler, and demonstrated an equal affinity with that composer too. The main work was the Fifth Symphony, and while it was obviously a young man's performance, with every colour heightened and every emotional shift consciously underlined, Franck also mapped the symphony's structure in a graphic and totally satisfying way.

It is rare to hear Mahler's Fifth so obviously divided into the three parts that the composer indicated in the score, and even rarer to hear a performance as leisurely as this one. Franck took more than 85 minutes over the work, with the central scherzo alone, which makes up part two, lasting longer than the average symphony by Haydn.

Yet miraculously it never dragged, even when the reprise of the first-movement funeral march was brought almost to a halt, or the last drop was squeezed out of the repeats in the scherzo. A few moments of roughness in the Adagietto suggested that the LSO strings had not always grasped exactly what Franck wanted, but Mahler's most realistically optimistic work was steered home with total assurance and conviction.

The sheer scale of the Fifth, and especially this monumental take upon it, might well have made the preceding Kindertotenlieder almost superfluous. But with Alice Coote as the soloist there was never a suggestion that this was a performance to be taken for granted. Coote made the audience hang on every troubled word of these songs; her tone was wonderfully even, her delivery unadorned and utterly direct. This country is peculiarly well-blessed with fine mezzo-sopranos at present; Coote could turn out to be the very best of them, if she is not that already.

A version of this review appeared in later editions of yesterday's paper.