OBJECTIVES: To explore whether the Screen and Treat Programme to support United Kingdom citizens potentially affected by terrorist attacks in Tunisia (2015), Paris (2015) and Brussels (2016) was effective in identifying and referring people to mental health services, to examine the programme's acceptability to users and to understand how agencies involved worked together. METHODS: Individuals offered screening by the programme (n = 529) were invited to participate in the study and were sent a questionnaire. Follow-up interviews were conducted with questionnaire respondents who consented and with employees of agencies involved in the programme's planning and delivery. Seventy-seven people affected by the attacks completed questionnaires, 35 of those were also interviewed, and 1 further person only participated in an interview. Eleven people from agencies organizing and delivering the programme and five clinician-managers were also interviewed. RESULTS: Most service users said the attacks had a major impact on their lives. Many reported anxiety, depression, difficulty going out or travelling, sleep problems, panic attacks, flashbacks and hyper-vigilance. A third had reduced their working hours and a similar proportion had taken sick leave. Two-thirds sought help from their General Practitioner (GP) before being contacted by the programme, but almost all thought their GP had not been helpful in dealing with post-traumatic stress disorder (PTSD) or referring to appropriate care. Several people were prescribed psychotropic medication; only a few were referred to mental health professionals. Many participants used help offered by organizations external to National Health Service, with mixed experiences. Waiting times for treatment varied from no delay to a few months. Most interviewees thought the programme should have started sooner and provided more information about sources of support. Most users found treatment received via the programme helpful. Professionals involved in organizing and delivering the programme thought that bureaucratic delays in setting it up were key limitations on effectiveness. Clinician interviewees thought an outreach approach was needed to identify at-risk individuals. CONCLUSIONS: Users who took part in the programme were satisfied with their treatment, although many thought it should have been offered sooner. Funding and data sharing between agencies were the main barriers to timely contact with affected individuals. Self-referral, GP identification of PTSD and GP referral to appropriate care were regarded as ineffective, suggesting that people affected by similar future incidents should be supported better and assisted more promptly to access treatment.