Leonskaja, BBCSO, Bĕlohlávek, Barbican Hall

Fantasies in apparent freefall, though in fact ruthlessly organised and blindingly well executed, were the name of last night's game - an endgame, as it happened, to the BBC Symphony Orchestra's hardest-working Barbican season before the marathon of the Proms.

Leonskaja's encore, the Chopin E flat Nocturne, might seem like an odd place to start. But it was very much the heart of the evening, convincing those who hadn't been lucky enough to catch her colossal Wigmore Hall Chopin recital last November that no-one could go deeper in this music. The audience silence was deafening as the Russian's spacious pianism came closer than any other performance I've heard to a lesson in transcendental meditation, a sacred rite.

In the Schumann Concerto, Leonskaja's statuesque figure poised effortlessly over the keyboard, rolling over the fiercer octave writing without fuss, blending in true concertante style with her woodwind colleagues (lovely, equally supple playing from clarinettist  Cho-Yu Mo). The majesty was somehow thrown off balance briefly in the finale - maybe because Leonskaja is known to do unexpected things in the heat of the performance, and BBC chief conductor Bĕlohlávek's elegant companionship seemed temporarily discombobulated - but it recovered for a scintillating coda.

Schumann's superficially free flow proved a good match for the other glorious outpourings in a programme better balanced than some of the monsters we've been exhausted by in recent weeks. Tippett's Fantasia concertante on a theme of Corelli is all frilly radiance with a dash of angostura bitters. In a way it's not surprising that Sir Malcolm Sargent trashed its objectives and refused to conduct the 1953 Edinburgh Festival premiere; it does seem frankly bizarre that whole string sections have to play fiddly ornamentation fit for only a single player. But maybe that was the desired effect in the fraught central fugue, which the collective BBC strings, sounding better than ever under Bĕlohlávek's training, executed dazzlingly.

I'm glad so much spotlight is being placed on the orchestra's world-class solo strings. Earlier this year we had one leader, Andrew Haveron, playing Korngold's Violin Concerto; his colleague, Stephen Bryant, is slated to play a Glanert work next season, and took the first violin role in the Tippett. Both the second violinist,  Amyn Merchant, and the cellist, Graham Bradshaw, play in two different quartets run by BBC players. Their joint, modified rapture in Tippett's deservedly famous Pastoral variation was very much in line with Bĕlohlávek's flowing, unfussy approach.

Yet it was the grand finale of his Martinů symphonies series which many had travelled from all parts of the country to hear. What we've learned over the past eight months is that there isn't a dull bar in any of the six masterpieces the Czech composer wrote in his American exile. No. 6, the Fantaisies Symphoniques, used to be declared the greatest of all (and the best known thanks to Kenneth MacMillan's brilliant choreography in the last act of the Royal Ballet's Anastasia); now we know it was just another way for Martinů to examine in unified symphonic form his preoccupations of love and loss. While the first five flowed from his pen at yearly intervals between 1942 and 1946, seven years elapsed before he turned to the Sixth.

Why the delay? A near-fatal 20-feet fall from a balcony at a summer music school had left him unable to walk and to work properly, though of course his irrepressible and prolific nature was hardly still for long. A stream of chamber works, small-scale gems with big things to say, kept him busy. Eventually it was Charles Munch, flexible French master of the Boston Symphony Orchestra, who inspired the Fantaisies as a kind of homage to Berlioz: Martinů originally wanted to call the work "New Fantastic Symphony", and I'm indebted to an email correspondence with Sir John Eliot Gardiner, who recently conducted the work in Prague and will do so again at the Proms, in which he pointed out a passage in the finale which is an exact replica of the first-movement conclusion in the Symphonie Fantastique.

Martinů's fantastical sense of orchestral colour is certainly a kind of 20th century equivalent to Berlioz's; the middle movement is a nightmarish kaleidoscope of unorthodox instrumentation. But what Bĕlohlávek drove home so piercingly in a work he knows so well he conducts it from memory is the requiem-like nature of the finale. We need that elegy after so much busy-ness; but the tumultuous cavalcade of memories from Dvorak, Suk and Martinů's own seminal work, the dream-soaked, memory-obsessed opera Julietta, is unexpected and collapses with shocking suddenness. If this was a performance of higher decibels than others in the series, always over-amplified by Barbican acoustics, it was also one in which the polished solo work of the indefatigable BBC orchestra reached new heights. Next season Bĕlohlávek will be taking a break from Martinů, but please, in the following year, could the concert planners see that he gets to tackle the even later fantasy worlds of the Frescoes of Piero della Francesca, the Parables and the Estampes? Because if this experience hasn't proved to a wider public that Martinů is a genius of the very first order, nothing will.