The Haim sisters are in high spirits, telling London how pleased they are to be here, how amazing the crowd is, how brilliant life is. It transpires the sisters from Los Angeles signed to Polydor over dinner just before the show; Haim are a group on a crest of a wave – in demand, adored and feeling capable of anything.

That, certainly, is the only explanation for the moment of pure cheese that sees them bring on their mum and dad – to sing and drum, respectively, on a version of Mustang Sally that you might expect to see in a pub, but not from the year's most hotly tipped band. Their unfeigned delight at playing with their parents means they are greeted with cheers rather than exasperated sighs. Not even a bass solo can diminish the goodwill.

Tonight's set is brief – just eight songs, and only six of them originals – but in their 40 minutes on stage, Haim offer enough to justify the hopes on their behalf. The suggestion that they're some sort of fusion of R&B and folk rock is revealed as a red herring on The Wire, a winning update of 80s US mainstream pop – all three sisters take lead vocal lines, overlapping and interleaving, and Danielle Haim's guitar flits from screeching solo to controlled arpeggio. That their musical homeland is closer to the arena than the dance club is signalled by their enunciation in the chorus: wire becomes "wyeeearrrr". A cover of Fleetwood Mac's Oh Well suggests a love of the heavy blues, too.

The next test will be playing longer sets, in bigger rooms, to more people: it's only the covers that stretched this show longer than their London debut, low on the bill, a few weeks ago. Nevertheless, for now, Haim are offering an unfettered and irresistibly joyful experience.