1 Tavistock and Portman NHS Foundation Trust, London NW3 5BA, UK; Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK. Electronic address: gskinner@tavi-port.nhs.uk.
2 School of Human and Health Sciences, University of Huddersfield, Huddersfield, UK.
3 Tavistock and Portman NHS Foundation Trust, London NW3 5BA, UK; Department of Clinical, Educational and Health Psychology, University College London, London, UK.