This paper examines how individuals form preferences on international trade and new trade agreements in the context of post-Brexit UK. We start from the premise that signing free trade agreements is a new and hard political issue, i.e. highly complex with undefined outcomes. We posit that, to form their preferences on such issues, individuals employ heuristics related to their subjective evaluations of their country’s relative strength vis-à-vis other countries or organisations. We test our hypotheses, using original observational and experimental data from two surveys representative of the UK population, carried out by YouGov in two time points (2019 and 2022), which confirm our expectations. Our findings have implications for the study of attitudes towards different aspects of globalisation and the role of heuristics in opinion formation on highly complex issues.