Background: A clear picture of people’s adoption of protective behaviours, and a thorough understanding of psychosocial correlates in the context of contagious diseases such as COVID-19, is essential for the development of communication strategies, and can contribute to the fight against epidemics. Methods: In this paper, we report a survey on the adoption of the recommended protective behaviours before and during the epidemic. We also assessed demographic correlates, and beliefs (towards COVID-19 and protective behaviours, towards SARS-CoV-2 transmission, social dilemma variables, and perceived external cues) of a representative sample of British residents. Data were collected during the early stage of the COVID-19 epidemic that spread worldwide in 2020. Results: Results showed a marked increase in the adoption of protective behaviour. We also identified targets for intervention in variables related to transmission of the virus and social dilemma-related beliefs. Sex differences in the adoption of protective measures, as well as differences associated with the frequency of social contacts, were associated with differences in beliefs. Conclusions: These findings suggest changeable determinants, which could be targeted in global communication about COVID-19, or in interventions targeting specific sub-groups not following the protective measures. © 2020 International Association of Applied Psychology