Vampire Weekend, Somerset House, London

London's pavements have just stopped resembling the ice-rink on which children spin, largely oblivious to New York's hippest band playing on the balcony above them.

"It feels just like Reading in August," Vampire Weekend's singer, Ezra Koenig, says, perhaps beginning to regret the most meteorologically challenged open-air gig in recent history. He blows on his fingers, so he can keep playing a guitar whose strings snap in the cold.

Somerset House's summer gigs will doubtless remain preferable for most, but seeing the winter skaters surrounded by eager young Vampire Weekend fans provides a surreal and wintry spectacle far more joyous than the sight of the band in Reading in August.

This free half-hour gig is part of a breathless two days of promotional activity for the band's second album, Contra, before a full UK tour next month. The vague controversy over Vampire Weekend's privileged background can be set aside. The new album's melancholy closing track, "I Think UR A Contra", plays with references to The Clash's equally privileged embassy brat, Joe Strummer, but no apologies are necessary. Vampire Weekend admit and alchemise where they are from, never more so than on "Walcott" – a dream of escape from Cape Cod, "all the way back to the Garden State" of New Jersey. Here, Vampire Weekend are privileged and provincial. The song is played tonight with a pure rush of release.

The softer and more complex music of Contra is omitted, however, in favour of infectious afro-punk party tunes such as "Holiday" and "Cousins". For all their subtlety, Vampire Weekend are the most simply enjoyable of the North American indie bands who have broken into the mainstream, which is surely something they learned from the afropop which is so crucial to their sound. The guitar and keyboards are high and light, a happy contrast to the gloomy neon glow of the sky. The lightly-worn intellect of the lyrics is at the service of a friendly good time.

On the archly named "Cape Cod Kwassa Kwassa", drummer Chris Tomson's African rhythms underpin Koenig's inarticulate cries of pleasure. Then, halfway through "Horchata", the whole hair-brained enterprise collapses as the power blows. Koenig tries semaphore to say goodbye, before the electricity allows a closing "Walcott" and everyone smiles through the cold.