Since the UK's vote to leave the European Union, there has been considerable debate about whether voters (particularly Leave voters) were well-informed prior to making their decisions. We gave a 15-item EU knowledge quiz to a large, nationally representative sample of the British population via an online survey. Our quiz included nine ‘ideologically neutral’ items, as well as six items that we deemed more ‘ideologically convenient’ for one side or the other. Overall, there was no average difference between Leave voters and Remain voters (either before or after controlling for covariates), despite the fact that Remain voters scored slightly higher on a short test of probability reasoning. In addition, both Leave and Remain voters were more likely to answer correctly on items that were ‘ideologically convenient’ for them. Consistent with the previous literature, older age, male gender, higher education, and stronger political interest were all significant predictors of EU knowledge. Interestingly however, these variables only predicted knowledge on the nine ‘ideologically neutral’ items; their associations with knowledge on the six ‘ideologically convenient’ items were generally weak and non-significant.