United Kingdom and the euro

The United Kingdom did not seek to adopt the euro as its official currency for the duration of its membership of the European Union (EU), and secured an opt-out at the euro's creation via the Maastricht Treaty in 1992, wherein the Bank of England would only be a member of the European System of Central Banks. United Kingdom opinion polls showed that the majority of British people were against adopting the euro; and in a June 2016 referendum, the United Kingdom voted to withdraw from the EU, significantly reducing any chance of future adoption.

Source: Wikipedia — United Kingdom and the euro (CC BY-SA 4.0)