Let’s not beat about the bush: the BBC Symphony Orchestra wouldn’t rank among my top ten orchestras in the world. It’s a dab hand at contemporary music, a staple of its regular diet at the Barbican, but for bread-and-butter repertoire it can churn out some variable performances. Semyon Bychkov, however, has a transformative power over its players and in a monumentally impressive account of Dmitri Shostakovich’s Leningrad Symphony that filled the vast expanses the Royal Albert Hall, Bychkov made the BBCSO truly sound one of the world’s greats.

Before the Shostakovich, the concert opened with Mozart at his most amiable, the two piano concerto K365, probably written for Mozart to perform with his sister, Nannerl. French siblings Katia and Marielle Labèque were the sparring partners here, facing each other across their keyboards. Katia is the more impish, the more impulsive pianist, leading to the occasional scrambled phrase; Marielle is the calmer presence. Bychkov, batonless, shaped the sensitive accompaniment, pulled threads of sound from his fingers as if manipulating a string puppet. As the Labèques chased each other through Mozart’s opening Allegro, then elegantly shaped the Andante, there was a hint of blandness about the performance, which evaporated in a hypnotic Philip Glass encore, dispatched with great style.

In September 1941, Shostakovich made a morale-boosting radio broadcast from the besieged city of Leningrad, announcing the completion of the first two movements of his new symphony. The Seventh, completed after the composer had been evacuated to Moscow, was a wartime rallying cry against the invading Germans, although later Shostakovich was said to have claimed (in Solomon Volkov’s book Testimony) that the symphony was about “the Leningrad that Stalin destroyed and that Hitler merely finished off.” Whatever the politics, it’s an epic symphony, running to an epic length. Bychkov has a tremendous feel for its architecture; he knows exactly where he’s going and exactly how he’s going to get there. Tempo changes always seemed just right and the attention to detail in orchestral colour was remarkable.

Strings had airy lightness at the opening of the first movement Allegretto, joined by carefree piccolo. The jaunty, banal “invasion theme”, which is treated to Boléro-like repetition and colouring amidst a lengthy crescendo, began unbelievably quietly. Bychkov had the side-drummer, who sets the pulse, cunningly concealed between harp and piano – barely visible and barely audible too. His baton beating strict time, the invasion gathered force, layer upon layer of sound building steadily, the brass and percussion rolling in to deliver an explosive climax at a thrilling pace. Just as fine was the bassoon’s lament which shortly followed, eloquently delivered by Julie Price.

While the woodwind section lacks the dark tone that Russian orchestras can bring to Shostakovich, there was plenty of sardonic indignation to the E flat clarinet outburst in the second movement. The strings were at their finest in the intensely aching Adagio, a threnody perfectly sculpted and balanced by Bychkov, sounding like a Bach prelude in response to the woodwind’s chorale. The finale was defiant, resolute, but never turning to bombast. Bychkov returns to the Proms right at the end of the season with the Vienna Philharmonic. Let’s see if they can match the BBCSO’s world-beating form.