The bookers for the series of summer shows at Somerset House have got one thing spot-on this year: almost every act, from rabble-rousing Bloc Party to trippy-dippy Sigur Ros to epic sentimentalists Starsailor, has proved ideal for the dreamy courtyard setting. For many bands, playing outdoors has had a bracing effect, and they're all the better for it. Or perhaps the combination of cobblestones and sky primes crowds to appreciate bands in a way that would be impossible at Brixton Academy in January.

Starsailor are lucky enough to have a catalogue that attains its full, slightly crazed grandeur when exposed to fresh air. Since 2001, when they were briefly the Next Big Thing, the Wigan foursome have grown into veterans who combine the best bits of Oasis, the Charlatans and Keane. It's odd that Keane somehow become so popular when Starsailor have been working exactly the same vein of tremulous emotionalism for five years - but if Starsailor are now the B team, their effect on audiences is exactly the same as the A.

Boys punch the air as regal choruses unfurl; girls do the same, but eye singer James Walsh purposefully. He is worth watching: without his high-pitched singing, this group would plod back to pubsville. He puts quavering flesh on the bones of piano ballads such as Alcoholic and Fever, and hits frenzied heights on the orchestral Silence is Easy, while displaying a sweetness that makes his diffident bandmates seem like a trio of Liam Gallaghers.

Walsh apologises for subjecting us to a song from the new album, reads out a request from a fan to sing at her wedding and brings an acoustic version of the Clash's London Calling to a halt when the lyric upsets him. "'London calling to the zombies of death' - Jesus, this is bleak." Only on a splendid, rousing encore of Four to the Floor does he swagger like a rock star, bringing this surprisingly lovely show to a happy conclusion.