With its powerfully emotive stagings of Bach's St John Passion and Verdi's Requiem English National Opera has built something of a reputation for bringing sacred masterworks to the secular stage. Award-winning director Deborah Warner, conductor and Handel specialist Lawrence Cummings, and ENO's indefatigable chorus master Martin Merry tell Edward Seckerson about the challenges of making a credible stage spectacle of Handel's Messiah, which opens on Friday 27 November.