On January 31, 2020, the UK left the European Union. Since the 2016 referendum, there has been a significant body of literature designed to answer the question of why the country’s residents made such a decision. This article contributes to scientific research on the subject under consideration. The novelty of the presented research is that, unlike most of the available works, it does not focus on the problems of migration and the deterioration of the socio-economic conditions of the country’s indigenous population. The article proves that these factors alone do not explain such broad support for Brexit by all segments of the population. The social transformation of the entire Western society, which led to the destruction of the usual social ties and traditional foundations of self-identification, is considered as one of the key reasons for the development of separatist sentiments in the UK. A person ceases to feel part of something whole and unchangeable, which causes a sense of fear, uncertainty and helplessness in many people, regardless of social affiliation. This forces us to look for a source of stability in the country’s past, when it was an independent and great Empire, which is embodied in the myth of “Global Britain”. The populist slogan “Take Back Control” is based on the historically insurmountable institutional differences between the UK and Europe, the main one being the UK’s attitude to the case law of the European court of justice, whose broad interpretations were included in the country’s administrative practice, which clearly contradicted the residents’ idea of democracy. Finally, author analyzes how these deep assumptions were embodied in the populist rhetoric of the “Leave” company, whose supporters used the post-truth methodology, offering a wide range of populist tools of both intellectual and emotional nature for almost all groups of the population, very accurately selecting information for various communication channels. The results of this study can be useful for analyzing nationalist and separatist sentiments in Western countries and predicting future developments.