Even Shostakovich’s admirers can’t agree about the composer’s Eighth Symphony. Is it the noble and tragic embodiment of Soviet Russia at war and under Stalin, or merely a series of effects looking for a cause? It’s a safe bet that conductor Valery Gergiev thinks it’s a magnum opus; it has become one of his signature pieces, a work to turn to on big occasions.

So it was last night, when he brought “his” band, the London Symphony Orchestra (he’s its principal conductor), to the Proms. Gergiev is not a man to waste time, and he didn’t even allow the applause to die away before setting the music in motion.

That sense of urgency ran more or less unbroken throughout the hour-long piece, the drama seeming to flow directly from Gergiev’s fluttering fingers to the players. The stunned mournfulness of the opening Adagio was not overplayed; flutes screeched, clarinets wailed, and Christine Pendrill drew out the aching moan of the long cor anglais solo without any sense of wallowing in it.

And so it continued. The Shostakovich code-breakers have all kinds of theories about what the symphony means; with playing as refined as this, the music could speak for itself. If the sheer length of the Adagio threatens to unbalance the whole piece, the intensity never slackened.

Gergiev is a conductor who relishes extremes, yet those extremes acquired a cumulative momentum, apparent in every passing detail. It’s not that Gergiev imposed logic on Shostakovich’s sometimes lurching mood-swings; rather, he followed them as if they made perfect sense.

The concert opened with another meaty chunk of Soviet music-making on the verge of dissidence. Alfred Schnittke was a student when he wrote Nagasaki, a steamroller of an oratorio that, fewer than 10 years after the event, tried to make sense of the atomic bomb. In the scale of forces that it requires, if not quite in achievement, the oratorio is even more monumental than the Shostakovich.

A huge chorus (here, the London Symphony Chorus) and sonorous organ added weight to the large orchestra, while at the other end of the scale, the theremin, an early electronic instrument, added its eerie whine to Schnittke’s dense patchwork of sound. The heart of the matter is a solo for mezzo-soprano; balancing between anguish and restraint, Elena Zhidkova caught perfectly the agony of a mother searching the ruins for her baby. Nagasaki had to wait 40 years for this, its UK premiere; in Gergiev, the LSO and Zhidkova, it had found ideal advocates.
Repeated Monday 7 September at 2pm. www.bbc.co.uk/proms