A jaunty little tune called 5 Years' Time has become the surprise hit of the summer, but Noah and the Whale might well prefer it to start going down the chart now. Otherwise, they could find themselves with a careerthreatening novelty hit on their hands.

"If there's one thing I'd like people to remember, it's that we're a real band," announced frontman Charlie Fink, perhaps fearing he'd created a monster by combining whistling and ukulele in one cute pop song.

In fact, the group from Twickenham were nowhere near as twee as that single might suggest. Instead, they demonstrated a robust, folkish charm along with some surprisingly powerful musicianship.

The Roundhouse has been transformed for the Colour Your Summer series of intimate gigs, with much of the audience seated at tables, although a problematic start meant Noah and the Whale sounded uncomfortably like a ropy cabaret act.

It was soon fixed, though, and Fink's plan became apparent: the brand-new debut album Peaceful, The World Lays Me Down was being performed from start to finish, with a few more violinists and a brass section for the occasion. It was a bold move that underlined the 22-year-old's musical maturity, as he switched naturally between stark, simple laments and barnstorming band efforts that swept you up like Arcade Fire's finest work.

Noah and the Whale were certainly able to induce feelings of euphoria but, given his lyrics, Fink also remembered the dictum that happiness writes white. "I will die and never ever hold your hand," he croaked on Second Lover.

Even 5 Years' Time was bittersweet, especially as Fink's sister Lily replaced the single's vocalist and his ex-girlfriend Laura Marling, whose Mercury-nominated album he produced. A gently chaotic rendition of that song got the crowd cheering and clapping at their tables and the cinematic Rocks and Daggers was equally endearing.

For the encore, Fink introduced a more rocking tune as the first track on their next album, although his guitar problems suggested perhaps he'd got a bit cocky. Still, in five years' time, it's a fair bet that he'll be a star.