Policies to promote public health are based on trust. There is a danger that public trust may be lost, especially where policies are seen to be influenced by vested interests or conflict with available evidence. Although trust in public health policies in the UK is high, some commentators have questioned recent responses to the threat of pandemic flu, suggesting that they may be driven, in part, by those seeking to profit from health scares, and drawing a direct comparison with terrorist scares. We argue that the approach to evidence by the public health and counter-terrorist communities differ markedly. Public health professionals must ensure that their actions do not undermine their credibility, in particular those involved in response to the threat of bioterrorism.