Simon Bainbridge's new orchestral work, Diptych, is in two parts that the composer says he would prefer to be heard separately. In this premiere performance by the BBC Symphony under David Robertson, they were positioned as the opening items in each half.

The first has its visual starting point in reflections of Venice seen in the canals when their surfaces break up and re-form. In Bainbridge's musical analogue, harmonic pillars dissolve into the polyphonic lines that form the music's surface, then solidify once more - a process repeated many times. Bainbridge's delicate harmonic and instrumental palette is finely deployed, though the repetition of one basic musical process over the 10-minute span does not really sustain interest.

The second panel is also concerned with fragmentation: here, of a large ensemble into three separate chamber-orchestra-sized units, which subdivide further into smaller groups and solos. Each group is given different materials - though, in practice, these were not sufficiently striking to register as powerfully as they needed.

In between the two halves, Barry Douglas was the soloist in Bartok's Third Piano Concerto in a performance that caught fire only in the finale. Elsewhere, his muscular lyricism was an asset, though he needed more focused backup from Robertson and orchestra.

They were at their best in the last work, Skryabin's Poem of Ecstasy. Whatever the mystical intent, it is the piece's frank eroticism that hits home. Robertson gave the players their head as it passed through a sequence of orgasmic climaxes, with the expanded brass section on particularly priapic form.