Valery Gergiev 's right hand flutters and shimmers. From a distance, the gesture seems unreadable. But, as one member of the LSO told me, "We don't understand how he communicates. But we always know what he wants us to do."

There was a time when Gergiev's appearances in London were rare. Each concert was a revelation and a sensation. He would, for example, conduct the operas of Rimsky-Korsakov, hardly ever performed outside Russia. Works such as Kashchey the Immortal (1902) and The Invisible City of Kitezh (1909) introduced London audiences to a world of of fantasy and sorcery, and music imbued with the spirit of late romanticism.

This Prom programme inhabited that same exotic sound-world. Scriabin may have been disdained by Rimsky as composing derivative music inspired by arch-conservative Anton Rubinstein, but in parts of the first symphony he cultivates a far more authentic voice. Stravinsky was a private pupil of Rimsky until 1908, and the influence of his teacher is all over Firebird (1910).

This Prom had definitely passed well below the radar of the London critics when they made their season's picks. Perhaps the name of Scriabin on the programme is a turn-off. He certainly isn't in fashion: according to Bachtrack, not a single note of his music will be heard in the 2010/2011 season at either the South Bank or the Barbican. And the later works can be forbidding.

Or perhaps the critics have now heard too much of Gergiev, take him for granted, even got tired of him. Whatever. His working relationship with the LSO has flowered. Whether giving audiences a taste for the different - Scriabin - or taking risks with the familiar - Firebird - the familiarity and the trust now allow Gergiev and his London orchestra to push the boundaries.

Scriabin's Symphony No 1 in E major (1899-1900) is the optimistic work of a man in his twenties. At its best - the slower movements - the melodies start airborne and reach ever higher. There is a lightness in the orchestral texture, gorgeous and very often bassless. There were plenty of opportunities for wind soloists - Andrew Marriner on clarinet, Gareth Davies on flute both on peak form - to float gorgeous sound over the orchestra. Bassoons and horns would hover underneath them in their higher registers to catch them.

Yes, there are weak points in the work. The thematic material in the fourth of the six movements is very slight indeed. Scriabin also clearly had problems with the ending: a final choral fugue in praise of art, to words penned by himself doesn't really work, it's an otiose way to bow out. But the richness of orchestral sound, the unanimity of the LSO's remarkable first violin section, and a common vision made this a performance to savour of a work seldom aired.

Firebird is the opposite of unfamiliar. It is an orchestral staple which sits under the fingers of every professional orchestra in the world. But a partnership like that of the LSO and Gergiev gives it a freshness and responsiveness to do the impossible and make its familiar surfaces shine anew. There is such trust between orchesta and conductor, nobody gets wrong footed. Soloists are given air and space.

The longer narratives hung together too, it was a performance which started strongly in the lower frequencies of the bass section playing in unison. And then just grew. Tempi were completely flexible. In this Rubato City there was gambling, edge-of-the-seat risk-taking. The pianissimo before the final horn solo was extreme, other-worldly, only spoiled by extraneous audience noise. The chattering and chirping of the upper wind in the faster sections was mesmerising. Years ago I remember playing those passages in an orchestra. All I can say is that we had fun trying....

The audience kept bringing Gergiev back to the stage with more applause after the performance. Gergiev raised that commanding right hand to get all of the soloists and sections of the orchestra to their feet one by one. But we didn't get the encore which this triumphant occasion deserved.