Mencap Little Noise Sessions: Snow Patron, Union Chapel, London

This latest acoustic bill in aid of Mencap has an easy, diverse charm. The headliners Snow Patrol play their part, but they are far from the highlight.

Instead, an imaginative, impressive performance by Cajun Dance Party should make them stars. The rail-thin, cherubic, 17-year-old singer Daniel Blumberg has the look, but not the arrogance, of mid-Sixties Dylan. His bell-clear voice can affect a high, angry shiver, but it deepens into gravel for the Velvet Underground's "Candy Says", the original's languid self-disgust turned into a salving lullaby. A string section made up of friends is more than an indie affectation; it's integrated into music that it swells and deepens. They've few songs to match this sound yet, but "The Hill, the View and the Light" has a mystic sense of shade and transcendence.

Roisin Murphy pops in next, at her best in the mixture on "Overpowered" of glacial cabaret and acoustic R&B. Declan O'Rourke follows, at Snow Patrol's request. A strong-voiced Irish singer-songwriter unknown in the UK, his comfortable ballads prove relaxing as the Chapel's stained-glass windows fall into shadow.

When Snow Patrol appear, Gary Lightbody is framed in a beam of light, and the white tie tucked into his black shirt looks very like a vicar's collar. But he seems freaked out to be in a place of worship, claiming he's never been to one before. "I don't wanna bring the rest of you to Hell with me," he cautions, after yet another burst of inadvertent mild blasphemy.

Funnier and more personable than on record, he digs deep into his band's songbook for this special show. The drug-addled excuses to a raging girlfriend on "How To Be Dead" ("I haven't made as many mistakes as you've listed so far...") is followed by an obscurity from their first album, the self-described "teen poetry" of "Fifteen Minutes Old", and the rarely played, diffidently conversational "You Could Be Happy".

A trio of covers includes the US indie band Low's "Just Like Christmas", suggesting reserves of ambition that Snow Patrol's own polite music steers clear of. They are likeable but unchallenging and musically unmemorable almost throughout this show.

For all Lightbody's discomfort with religion, "Chasing Cars" begins as a hymnal, Hebrew dirge before building into glistening pop. In the neon light, the crowd look like a rapt congregation. "Run", their most intentional anthem, is then reduced to the slowed melancholy of cello and voice. Snow Patrol's success remains an inexplicable wonder, but on this night they did themselves, and this cause, justice.