This study was funded by the Medical Research Council (MR/N028244/2). Professor Colin Drummond is partly funded by the NIHR specialist Mental Health Biomedical Research Centre at the South London and Maudsley NHS Foundation Trust and is an NIHR Senior Investigator. Professor Colin Drummond is partly funded by the NIHR CLAHRC South London at King’s College Hospital NHS Foundation Trust. The views expressed are those of the authors and do not necessarily reflect the views of the Department of Health, the National Institute for Health Research or the Medical Research Council.