Edge and Bono were on stage for a surprise acoustic set tonight for the Mencap Little Noise Sessions at London's Union Chapel. In a stripped down twenty minute performance, with Adam watching from the balcony, they played Stay, Desire, Angel of Harlem and Wave of Sorrow.

Presenter Jo Whiley asked the audience, who had come to hear We Are Scientists, Biffy Clyro and The Courteeners, to give a warm welcome for an up and coming act: the guitarist had not been playing that long and might make some mistakes while the singer was a little bit shy and not too articulate. 'Please welcome Edge and Bono!'

The audience provided a huge welcome for a haunting version of Stay, from 1993's Zooropa, which gave way to a pew-thumping performance of Desire, with Bono on harmonica, and segued into a timely rendition of Angel of Harlem. 'Our Christmas song,' explained Bono, on this cold winter's evening in north London.

With everyone demanding one more, Edge headed for the keyboards and opened up some chords to a U2 song never previously played live, Wave of Sorrow, found on the bonus CD of b-sides and rarities that comes with the remastered Joshua Tree. A song inspired, explained Bono, by his trip to Ethiopia in 1985. 'A really important time in the direction of my life and of the band.'

More soon.