Background Understanding COVID-19 risk perceptions and their impact on behaviour can improve the effectiveness of public health strategies in the future. Prior evidence suggests that, when people perceive uncontrollable risks to their health, they are less likely to make efforts to protect their health in those ways which they can control (e.g. through diet, exercise, and limiting alcohol intake). It is therefore important to understand the extent to which the threat of COVID-19 is perceived to be an uncontrollable risk, and to assess whether this perceived risk is associated with differences in health behaviour. Methods We surveyed a nationally representative sample of 496 participants, shortly after the peak of the pandemic in the UK. We collected data to assess people’s perceptions of COVID-19-related risk, and how these perceptions were associated with behaviours. We examined self-reported adherence to behaviours recommended by the UK Government and National Health Service to prevent the spread of the virus, as well as more general health behaviours. We predicted that increased perceived extrinsic mortality risk (the portion of a person’s mortality risk which they perceive to be uncontrollable) would disincentivise healthy behaviour. Results Perceived threat to life was found to be the most consistent predictor of reported adherence to measures designed to prevent the spread of infection. Perceived extrinsic mortality risk was found to have increased due to the pandemic, and was also associated with lower reported adherence to Government advice on diet and physical activity, as well as smoking. Conclusions Our findings suggest that promoting a message that highlights threat to life may be effective in raising levels of adherence to measures of infection control, but may also have unintended consequences, leading to a reduction in health-promoting behaviours. We suggest that messages that highlight threat to life should be accompanied by statements of efficacy, and that messages evoking feelings of concern for others may also be effective in promoting compliance with anti-infection measures.