This is the text of a communication given at a study day (journée d'étude) on "Borders" (Frontières), organised by the Language Department (Département des langues) of the Université Paris 1 Panthéon-Sorbonne. This study day took place on 1st June 2023, in the Turgot lecture hall of the Sorbonne. The communication reviews succinctly the causes and consequences of the Brexit referendum held in June 2016. Among other things, it points out the role played by the issue of immigration during the referendum campaign and the call to re-establish control over Britain's border with the European Union. The communication also sets out the fallacious arguments used by the Leave campaign about the advantages of quitting the European Union, as well as the plain ignorance and insouciance with which the "Brexiteers" set about what they were doing. It ends by noting that even by mid-2023, Brexit was still not finally "done", and that its impact on the UK economy has clearly been revealed as negative. The communication concludes with a short reflection on the weaknesses of using a referendum to carry out such fundamental policy change.