MacMillan premiere, Repin, LSO, Gergiev, Barbican Hall

"There is not one idea," wrote that intemperate critic Eduard Hanslick about Richard Strauss's Till Eulenspiegel, "that does not get its neck broken by the speed with which the next lands on its head." Rather a compliment, I've always thought, and certainly so as applied to James MacMillan's new Violin Concerto. As soloist Vadim Repin and conductor Valery Gergiev whirled us tumultuously through its hyperactive songs and dances, there was so much I wanted to savour, to hear again.

On one level it's a brilliant tour de force which does everything a virtuoso could wish, combining some of the fast, furious, fiddling reels complete with signature drum the bodhrán which are in MacMillan's musical DNA with the necessary chance to let the violin sing - and how, in Repin's dazzling, pitch-perfect performance. Nothing stays the same for long, not even in the dreamlike central Larghetto, where any worries that the composer will let woodwind and soloist sit too long on sentimental songs are quickly banished by the kaleidoscopic revolution of events. Little did I think that only days after the quick-change fantasies of Martinů's Sixth Symphony I'd be listening to another work which demands alert, quicksilver listening.

Deep down, the new concerto is also a memorial, remembering the songs MacMillan's late mother taught him. Innocence gets tangled up in the web of memory; bitter experience several times tries to blast away the nostalgia, climactically so in the finale. Exactly what the sources are the composer hasn't told us yet - nor why in the finale some of the men in the orchestra ask "Mutter" to dance in German verse, answered across a great distance of nursery rhymes and pop songs by some of the ladies. Death enters the mix with that ubiquitous Latin chant the Dies Irae. Sometimes troubling, then, but always entertaining - a great concerto to introduce kids to the wonders of a first-rate fiddler and a giddying orchestral fabric with lashings of exotic percussion.

It seemed to fit very well into a typically dense and challenging Gergiev programme: did MacMillan know that his work was to follow Stravinsky's Symphony in C? At any rate there's almost a quotation of that chameleonic work's opening gesture towards the beginning of the concerto. True, Stravinsky's fabulously clean and unorthodox palettes made his successor's orchestration seem a bit thick in places, but they came over with unusual heft in Gergiev's full-on, fluttering-fingered dynamism (gone is even the toothpick that for a while replaced the baton; both hands now do all the shaping).

It's hard to believe that this sometimes playful, and in last night's performance often very funny, celebration around the key of C came out of tragedy. At the time of composing it in 1938-9 Stravinsky lost his eldest daughter, wife and mother to the tuberculosis that nearly killed him too; if they are commemorated anywhere, it's in the sublimely detached exchanges of oboe, bassoon and trumpet in the air-treading Larghetto concertante. I confess I still don't understand the point of the scherzo: "Are you taking the piss?" seems to be the only possible response here. But the finale seems full of religious feeling, framing a lather of strings in which Gergiev drew stunning results from the LSO players with hieratic chords and a transfigured memory of the opening C.

Dedicating his symphony "to the glory of God" - another MacMillan connection - was a deliberate parallel on Stravinsky's part to the Symphony of Psalms composed nearly a decade earlier. That had the second half of a long programme to itself, with Gergiev surprisingly detached and the LSO Chorus hardly on the most focused form. The best moments came when their psalm singing was most expressively reinforced by the unorthodox assembly of cellos, basses and woodwind ranged so carefully in front of them: communal plaints and praises in which the instruments sang as full-heartedly as the choir.

So we ended with a mystery, and we began with one, too, so perfect that it would have been enough in itself. Gergiev has included Debussy's Prélude à l'après-midi d'un faune many times in various programmes; the last time I heard him conduct the LSO, it served as preface to The Rite of Spring. Being the great creative conductor that he is, the interpretation never sits still. On the previous occasion, the coda was the slow burn, a sense of loss transcendently realised. Last night it was all very measured, Gareth Davies's flute solo emerging from nothing and the beautifully painted gauzes remaining down throughout. Some found it all too slow, but for many of us it was pure concert-hall magic. In our programmes was a slip of paper telling us "Valery Gergiev has been named by Time magazine as one of the 100 most influential people in  the world". Minutes into the concert my cynicism about that vanished and I was more than happy to be under the influence.

• The concert will be broadcast by BBC Radio 3 on 20 May
• Gergiev repeats most of the programme, with Ravel's G major Piano Concerto replacing the MacMillan, in the LSO concert on 19 May
• Details of the LSO's 2010-11 season