Objectives. Behavioural responses to influenza pandemics can significantly influence the impact on public health. Protection motivation theory (PMT) provides a framework for understanding how people respond to health threats such as pandemics. The main aim of this study was to model the relative contribution of the components of PMT (threat and coping appraisal) to intentions to perform two behaviours recommended by the UK government in a pandemic: stay at home when ill and keep going to work when well. Design. A 2×2 factorial design was used to test the effect of scenarios describing pandemic severity (low vs. high threat) and advice messages (standard government advice vs. theory-based advice) on measures of threat and coping appraisal, and intentions to carry out the two recommended behaviours. Methods. A web-based survey designed to assess threat appraisal, coping appraisal, and behavioural intentions was completed by 883 adults (December 2009–January 2010) drawn from University College London staff and the local community. Structural equation modelling was used to test the PMT framework. Results. Perceived pandemic severity influenced threat and coping appraisals and intentions. Structural equation modelling revealed that coping appraisal (i.e., perceptions of the costs, benefits, and feasibility of the recommended behaviours) was the principal predictor of variability in intentions for both behaviours and for both pandemic scenarios. Conclusions. Coping appraisals appear to be an important, and hitherto underresearched, predictor of how people may behave in pandemics, and our findings provide encouraging preliminary evidence that it may be possible to change these perceptions.