Mozart was a famous improviser, much admired for the impromptu piano pieces he included in his public performances. But, by their very nature, such spontaneous outpourings have not come down to us, except in the form of transcribed fantasias that, it is supposed, adopt similar strategies. Angela Hewitt began her imaginatively conceived all-Mozart programme with two examples of these, both left incomplete by the composer and put into publishable form by Maximilian Stadler, who was musical adviser to Mozart's widow.

Hewitt's approach was aptly rhetorical, maintaining some sense of extemporisation in music whose content is necessarily less predictable and whose formal boundaries more fluid than, say, the sonatas. Both K396 and 397 are dramatic, minor-key works, and Hewitt's playing had a boldness and grandeur of scale that matched their emotional spectrum well.

But sometimes there was a suggestion of brittleness to her tone where mellowness or depth were needed, a fault that carried through into the two sonatas on the programme, the F major K332 in the first half and the C minor K457 in the second. Both had been considered from the point of view of the varied character of their material, but some of the shifts from one colour or texture to another were on the hasty side.

The tricky little Gigue K574 - which as her teacher, Jean-Paul Sevilla, mentioned in his programme note, is perilous - caused Hewitt to stumble, and the B minor Adagio lacked intimacy and pathos. She was absolutely secure in the variations Mozart wrote on the tune everyone knows as Twinkle, Twinkle, Little Star, but which he knew as "Ah vous dirai-je, maman." Either way it's a trivial thing with which even Mozart could do nothing interesting, and despite Hewitt's best efforts, she was unable to convince us to the contrary.