Policing is considered a highly stressful role, and police officers are at risk of mental health issues during their service. This is an area which has gained increasing attention in recent years, but further research, using validated measures, is needed to help identify other factors that are important and ensure further development as well as evidence-based, bespoke intervention. The current study sought to explore the general prevalence of stress, depression and anxiety in a UK sample of police officers, to examine whether length of service moderates the effects of stress, depression and anxiety, and whether certain personality traits protect against these. A self-report questionnaire was completed by 177 serving UK police officers from 10 different regions. Results revealed clinical levels of anxiety and depression, and comorbid presentations of major depression and anxiety, at rates significantly higher than reported in the general population. Results indicated officers are most at risk of experiencing stress during the first 15 years of their service, and that officers’ stress was organisational rather than trauma related. Additionally, officers higher in traits of extraversion and lower in neuroticism reported lower anxiety. The results of these findings are discussed, and suggestions have been made based on the current findings.