The UK’s departure from the EU is a pivotal moment in the history of Europe. The United Kingdom and the European Union has a longstanding relationship going back to 1973; however, against all expectations, in a referendum on June 23, 2016, the British people voted to leave the EU. According to the referendum result, more than 51.9% of the voters voted to leave. There is a hypothesis that British national identity can be the source of UK hostility to European integration. The main question to be posed here is that, how the unique formation of British identity drove the majority of people to vote in favour of leaving the EU in the 2016 referendum. In order to achieve this objective, Social Identity Theory has been applied as the main theoretical framework. Moreover, this study employed a qualitative methodology, and data was gathered from the existing survey polls such as Ipsos MORI, Eurobarometer and British Social Attitudes (BSA) surveys. The findings of this paper indicated that British identity has not been Europeanised as much as other European countries yet, and Britain’s weak sense of European identity was a key contributor to the Brexit vote.