U2 stars Bono and The Edge played at an unannounced warm-up act for a charity concert in London on Friday (23Nov07). The duo stunned the 250 guests at the fundraiser for Mencap, a charity that campaigns for equal rights for children and adults with learning disabilities. Bono joked with the audience, "Don't tell Larry (Mullen) and Adam (Clayton) we've done this," after performing four of the band's hit tracks.