At 79, Thea Musgrave is the undisputed doyenne of British women composers, and she's still busily productive – a fact which may have something to do with her residence in California. "The cool air agrees with me out here in Los Angeles. A good Scots girl could never be happy on the East Coast in summer," she says.
Her voice may not have much Scottishness now, but the work that she's about to unveil takes her right back home. Two's Company is a double concerto for the oboist Nicholas Daniel and the percussionist Evelyn Glennie, and arose out of the fact that the two are neighbours; plus the fact that Musgrave felt a double concerto might be fun.
"They are very different instruments, and don't mesh much," says Musgrave. "So I thought, why not dramatise that? I decided the percussion could have different set-ups so that Evelyn could walk round the orchestra. Then I thought, why shouldn't Nick walk round too? Thus emerged what is really a musical love-story. She starts downstage left with tam-tam and gong, but playing very softly, while he is off-stage. He comes on in response to the sound.
"The clarinets then have solos, which attract him to stand beside them. Evelyn is upset, and moves upstage behind the brass to get closer to him. Then he gets waylaid by the horns and harp, which annoys her even more. So she goes to a big bunch of drums, and a fierce exchange follows, Evelyn playing very loudly while he plays lyrically with the horns and harp. These interchanges get shorter and shorter, until, after a big outburst, he invites her downstage. Then a very romantic duet starts softly, and ends exultantly.
"These two players are so fabulous technically, and so charismatic – I can't wait to see what they will wear."
See Prom 63 at the Royal Albert Hall tomorrow. BBC Proms, to 8 September (020-7589 8212). Visit www.independent.co.uk/promcast for exclusive daily podcasts and listen online to highlights from the previous night