This paper explores the influence of Eurosceptic print media on public opinion regarding the European Union and the mechanisms through which individuals process information obtained from the news. Focusing on the 2016 Brexit referendum in the United Kingdom, we investigate the rejection of pro- Brexit messages in London despite a strong media bias in favor of Brexit. Our study aims to quantify the ‘filter hypothesis,’ which examines how media influences public opinion, by considering the composition of people's discussion networks (homogeneous or heterogeneous) and the media content (congruent or dissonant with the group's beliefs). Using a social simulation approach with GAMA, we create and analyze different scenarios to assess the possible direct and mediated effects of media on opinions about Brexit. Our findings suggest that in districts where most people intended to vote to remain in the EU before the referendum campaign, when the influence of the media is mediated by people's discussion networks and group pressure mechanisms, the simulation results are more in line with the actual referendum vote. Conversely, in districts where the majority intended to vote to leave before the campaign, the media exerts a more direct effect on opinions, seemingly not conditional on interpersonal communication. We offer a potential explanation for how Londoners resisted the persistent and unbalanced pro-Brexit media messaging. Our study contributes to the literature on Political Communication and Public Opinion about the EU, and we introduce a new computational methodology to quantify the mechanisms of the ‘filter-hypothesis’. We highlight computational social science's analytical and exploratory value. Our research sheds light on the formation of opinions about the EU and emphasizes the need for further exploration in this area.