Marianne Shawe-Taylor1, Michael Grant1, Zain Chaudhry2, Alexander Harper3. 1. St Bartholomew's Hospital, Barts Health NHS Trust, London EC1A 7BE, UK. 2. Guy's and St Thomas' NHS Foundation Trust, St Thomas' Hospital, London SE1 7EH, UK. 3. Whipps Cross Hospital, Barts Health NHS Trust, London E11 1NR, UK.