1Academic Department of Psychiatry, Charing Cross and Westminster Medical School, 24 St Dunstan's Rd, London, W6, UK
2Academic Unit, Horton Hospital, Long Grove Rd, Epsom, Surrey, KT19 8PZ, UK
3Maudsley Hospital, 99 Denmark Hill, London, SE5 8AF, UK
4Academic Department of Psychological Medicine, Royal London Hospital Medical School, London, UK