The Brexit, UK’, s withdrawal from the EU in 2020 was a pivotal moment in the history of Europe. The United Kingdom and the European Union have a longstanding relationship, which dates to 1973,however, against all expectations, in a referendum on June 23, 2016, more than 51. 9% of the BRITISH people voted to leave the EU. Certain scholars believe that the BRITISH national identity was one of the sources of the UK hostility toward a European integration. An important question to discuss regarding this hostility is: how did the unique formation of the BRITISH identity drive the majority of people to vote in favour of leaving the EU in the 2016 referendum? This question is investigated in this research through the theoretical framework of the Social Identity Theory. Relying on a qualitative methodology, data was gathered from various survey polls, such as Ipsos MORI, Eurobarometer and BRITISH Social Attitudes (BSA) surveys. Findings indicate that the BRITISH identity has not been Europeanised as much as other European countries yet, and that Britain’, s weak sense of European identity was a key contributor to the Brexit vote.