MUSIC/ Out of the egg: Anthony Payne hears Sibelius at the 'Tender is the North' Festival. Plus Mozart switched

Despite their high critical standing, only three of Sibelius' seven numbered symphonies are performed with any frequency in our concert halls. For that reason alone the Barbican Centre's 'Tender is the North' (a Scandinavian festival offering the complete cycle) has to be reckoned an event of unusual importance. But there is a bonus in that other rarer items of great power and originality have also been included, notably the tone-poem for voice and orchestra Luonnotar, which appeared in the opening concert, and that tragic heroic masterpiece of the 25-year-old composer, Kullervo Symphony, which was heard on Sunday, Finland's independence day.

Luonnotar is certainly one of Sibelius' most extraordinary works. This setting of words from the Kalevala tells a mysterious story of creation: after the mating of air and water, a gull's egg splinters in the ocean, producing heaven, moon and stars. The musical images which this myth drew from Sibelius are like nothing else in his output, except perhaps for the tremolando string opening which suggests Luonnotar herself, the virgin daughter of the air, in her breezy flight. The soprano's agonised, keening line, and the unprecedented harmonies of the closing sequence delineate new worlds of feeling, and the uncanny suggestion of an existence before the dawn of time remains one of Sibelius' most remarkable achievements.

The extraordinary concentration of language and structure achieved in Luonnotar was splendidly served by Sir Colin Davis and the London Symphony Orchestra, while Karita Mattila suggested some force of nature in the inhuman cantabile which she floated so effortlessly above the orchestra.

The bold expansiveness of Kullervo Symphony, with its five movements of orchestral, choral and solo vocal music, marks the opposite pole in Sibelius' symphonic development, suggesting that he was destined to follow a Mahlerian path. As it turned out, concentration and classical purity of expression were to be his destiny rather than an all-embracing diversity, but, paradoxically, Kullervo remains an utterly characteristic masterpiece. Consistently underestimated by commentators who probably had no chance to check their findings against a live performance, it only emerged as a major achievement after receiving its premiere recording some 20 years ago.

It remains unperformed in our halls, however, and Sir Colin and the LSO's interpretation with magnificent contributions from Soile Isokoski, Jorma Hynninen and the men of the Helsinki University Choir will surely be counted one of the musical events of the year. Sir Colin brought great splendour to much of the score, and there was a spine-chilling intensity in those passages of true daring where Sibelius extends ostinato figures into a trackless waste of sound - not much joy for the strings here, but the LSO stuck to their task manfully.

The tragic third and fifth movements, which set words from the Kalevala telling of Kullervo's unknowing incest and subsequent guilty suicide, were magnificently delivered, while the second, concerning Kullervo's lonely youth, balanced to perfection the irreconcilable facts of loneliness and serenity. If one felt any reservations about the performance they concerned the tempos adopted in the two quick movements. The first would have carried greater weight and revealed more of its textural magic at a statelier pace, while the tumultuous fourth, 'Kullervo goes to battle', lacked urgency. Still, this was an unforgettable occasion, and to cap it Finland's independence was celebrated with a rousing Finlandia, the choir majestic in its famous central hymn.

Festival continues until 13 December. Bookings: 071-638 8891