The two European referendums of 1975 and 2016 are examined in their historical, political and constitutional context. The paper provides a short account of United Kingdom’s accession and participation in the European Union. The uneasy relationship with the EU is shown, with reference to political process of negotiating Britain’s position in the Union. Some political, economic and cultural factors that have shaped British attitudes towards European integration are analysed. A legislative framework for both referendums is described and the dynamics of pre-referendum debates and campaigns are discussed. The political implications of ‘Leave’ vote (in favour of Brexit) are indicated. Finally, certain constitutional and legal issues surrounding UK withdrawal from the EU are considered, also in the context of the doctrine of parliamentary sovereignty.