Authors: Margaret May; Mark Gompels; Valerie Delpech; Kholoud Porter; Frank Post; Margaret Johnson; David Dunn; Adrian Palfreeman; Richard Gilson; Brian Gazzard; Teresa Hill; John Walsh; Martin Fisher; Chloe Orkin; Jonathan Ainsworth; Loveleen Bansi; Andrew Phillips; Clifford Leen; Mark Nelson; Jane Anderson; Caroline Sabin Journal: BMJ Date: 2011-10-11