British civil servants have a clear constitutional duty to obey their ministers. Yet civil servants may be confronted with situations in which they believe, on the basis of their knowledge or expertise, that the course of action a minister favours would have sharply damaging consequences for the government or the country. What should higher civil servants do then? We use data gathered in two rounds of interviews with senior civil servants (Grades 1–3) in 1989–90 and 1993–94 to explore how far civil servants feel able to go in challenging either inappropriate ministerial requests for services or policies they believe to be sharply damaging. Senior civil servants are divided on the appropriate course of action in such circumstances.