The current study evaluated a new training programme developed for generalist police who interview adults. It was designed to enhance officers’ use of open-ended questions with adult witnesses. The programme included all key training activities that had been used in successful earlier training evaluation studies related to the interviewing of child complainants of abuse. A total of 90 officers (recruits, n = 26; frontline, n = 37; and investigators, n = 27), completed the course over 6–12 weeks and their standardised mock interviews were analysed for open-ended question usage as well as auxiliary behaviours designed to support a narrative. Interviewer performance increased over time from baselines of 6–18% open-ended questions to 70–76% following the programme. Although there was a drop in performance at least 6 months after the training ceased (with no intervening follow-up sessions) (M = 9.02, SD = 3.07), performance was still significantly better than baseline, and the improvements in open-ended question usage were associated with improvement in broader interviewer behaviours known to enhance narrative detail such as the use of minimal encouragers. The practical implications of these findings and directions for future research are discussed.