Although consumers' growing interest in ethical consumption has been well-documented, their understanding of specific claims, and the link between their stated concerns and behaviour, has not. Using a framework from systematic-heuristic and behaviour modification theory, this study explored consumers' understanding of varied ethical claims and a specific eco-label, and then estimated the effect these stimuli had on their choice behaviours. In-depth interviews revealed a strong interest in environmental and social attributes but considerable scepticism about specific claims. However, a choice modelling experiment found ethical attributes nevertheless influenced respondents' choices. Two distinct clusters whose views and choice behaviours differed markedly existed: one was primarily price-driven and the other more responsive to specific claims. Discrepancies between the qualitative and quantitative studies appear attributable to differences in information processing; many consumers respond strongly to heuristics, even though they believe themselves sceptical of the claims these communicate. The findings raise important policy questions about the scientific basis of many ethical claims, since consumers were strongly influenced by these, despite their views to the contrary.