The level of anticipation at the Union Chapel on Friday night seemed excessive for an evening of acoustic music headlined by moody Scottish trio Biffy Clyro.

But Little Noise Sessions was hiding a big secret. It was left to Jo Whiley, the evening's obsequious curator, to introduce the mystery guests. "The guitarist, Dave, has only been playing for a few weeks, and the singer, Paul, is really shy", she said - and up strolled two of the biggest egos from the biggest band in the world, Bono and The Edge of U2.

Bono's rich tenor filled the Chapel's high ceilings during set-opener Stay (Faraway, So Close!), while The Edge's guitar-playing, usually laden with effects, was still effective in acoustic mode. Desire lost none of its energy as a folk-rock barnstormer, and Bono's harmonica-playing had the audience on the edge of their pews.

Though he must have been tempted in the Chapel's pious surroundings, Bono kept the sermonising to a minimum. "I won't bore your ass with the details," he joked during a rambling introduction to Wave of Sorrow, a track performed in public before.

Originally intended for the band's 1987 album, The Joshua Tree, the powerful ballad still sounded like a lost hit 20 years on.

Up next was little Liam Fray of The Courteeners, whose wry indie pop sounded rather exposed; following him, We Are Scientists' set was finely honed.

Official headliners Biffy Clyro prompted a mass singalong with their recent single Machines, though for much of their angst-ridden mid-tempo set, attention shifted to how hard the Chapel's seats were.

But it mattered not. The evening was already a huge success. And with respect to the other bands, this would have been the case with or without you.