BBCSO / Belohlavek, Barbican Hall, London<br/>Take the Risk, Purcell Room, London

We could have held a party for the composer's friends, but we just had a bag of M&M's

The long, wry face of Bohuslav Martinu gives little away. Posed for a studio portrait, cigarette clamped between his fingers, standing to the side of a concert poster in Boston or strolling through Central Park, here is a quiet man from a small, distant country.

Neither a forgotten genius nor an also-ran, he is a hard sell: fluent in several musical languages, yet somehow voiceless. Forgivable then, if regrettable, that instead of using their six-concert cycle of Martinu's symphonies to provide a context for this Czech chameleon – programming works by Pavel Haas, Erwin Schulhoff, Viktor Ullmann, Hans Krasa or Martinu's pupil and lover, Vitezslava Kapralova – Jiri Belohlavek and the BBC Symphony Orchestra launched their Barbican series with three other composers whose names begin with M.

Are there hints of Mozart, Mahler or Mussorgsky in Martinu's First Symphony? No. Premiered in Boston in 1942, the symphony sounds exactly as it is: a work by an experienced Czech composer writing for a large American orchestra. Rarely is there a phrase without some "added value", be it the skittering of a harp in high register, or the sparkle of a cymbal, like the nervous flourish of a chef who cannot serve a salad without garnishing it with a slice of orange and a snipping of chives. Yet the writing is undeniably polished and attractive. Moravian dance rhythms jostle with the melancholy flutterings of water and wood nymphs, ancient subjects distorted through the crazy-mirror sonorities of Expressionism and the smart syncopations of Broadway.

Big-bosomed, vampish melodies for horn and long-legged oboe solos cede to hazy, pastoral string writing, while snare drums signal Czech resolve under Nazi occupation. There's sorrow here – most evident in Belohlavek's meticulous sculpting of the Largo – and nostalgia too. But tempting as the parallels are between this and Dvorak's Ninth Symphony, Martinu, who had left Prague back in 1923, was suffering from something more complex than the homesickness that dogged his forebear in America. By the time his symphony was premiered, Kapralova, who had conducted the BBC Orchestra in 1938, and Schulhoff were dead, while Haas, Krasa and Ullmann had been interned in Theresienstadt. By the end of the war, Martinu would be the only leading Czech composer of his generation left alive.

Those anxious to hear the music of Martinu's contemporaries will have to search elsewhere. In the meantime, one has to hope that the insurance policy pieces in the BBCSO's performances of his Third, Fourth, Fifth and Sixth Symphonies (the Second was given this Friday) are better rehearsed than those here. Gerald Finley sang four songs from Mahler's Des Knaben Wunderhorn with unusual delicacy and restraint, saving himself for the tar-boiling malevolence of Shostakovich's orchestration of Mussorgsky's Songs and Dances of Death. Michael Cox's sensitively shaded flute playing was a welcome distraction from the diffident strings, whose lacklustre sound and scruffy entries of Mozart's Symphony No 29 indicated they might need m-m-more than two weeks' holiday after the Proms.

Renamed Take the Risk and curated by lutenist Paula Chateauneuf, this year's Early Music weekend at the Southbank Centre saw a convocation of chitarrones, cornetts, viols, harps and hurdy-gurdys explore historically informed improvisation from several centuries. At one end were the first parallel fourths of organum plainsong, from the Orlando Consort, and at the other the the bowed accompaniment of dramatic laments from 17th-century Rome, from Atalante. In-between we were acquainted by Crawford Young and Friends with the oral traditions of Sephardic song, and witnessed The Division Lobby's on-the-spot creation of an aria over a passacaglia.

As passionate as the Wagner Society, though more polite, the audience was as international as the performers. And for those who quibbled over what improvisation means in the context of figured bass, historical treatises and music stands, there was a chance to try it for themselves in Chateau-neuf's workshop.

If my hard-nosed self would have liked to have heard some improvisations in the style of Mozart, Liszt or Rachmaninov (the tradition lasted past the conventional Early Music cut-off point), Chateauneuf's gentle shepherding of 10 amateur instrumentalists through their first collective bergamasca was very nearly the highlight of this provocative, fascinating weekend. For extravagant, exotic beauty, however, it has to be the funerary soundworld of Atalante's lirones, viols, lutes, harp and organ playing Rossi and Marazzoli's opulent "vanitas" laments.