[1] UCL, Res Dept Behav Sci & Hlth, Gower St, London WC1E 7BT, England
[2] Harvard Univ, Harvard TH Chan Sch Publ Hlth, Ctr Populat & Dev Studies, Cambridge, MA 02138 USA
[3] UCL, Inst Canc, Canc Res UK & UCL Canc Trials Ctr, 90 Tottenham Court Rd, London W1T 4TJ, England
[4] St Marks Hosp, St Marks Bowel Canc Screening Ctr, Watford Rd, Harrow HA1 3UJ, Middx, England
[5] NHS England London Reg, 105 Victoria St, London SW1E 6QT, England