Countries who have seen usage of Euro

Greece
Greece was in debt crisis since November 2011. It is primarily  for the country or its government to deal with its public debt. The controversial and much discussed possible exit is often referred to in financial circles as "Grexit", a portmanteau combining the English words "Greek" and "exit". The term was coined by the Citigroup economist Ebrahim Rahbari and was introduced by Rahbari and Citigroup's Global Chief Economist Willem H. Buiter on 6 February 2012. Proponents of the proposal argue that leaving the euro and reintroducing the drachma would dramatically boost exports and tourism and encourage the local economy while discouraging expensive imports. Opponents argue that the proposal would impose excessive hardship on the Greek people, cause civil unrest, destabilize and harm the reputation of the eurozone, and could cause Greece to align more with non-EU states.

United Kingdom
The United Kingdom entered the European Exchange Rate Mechanism, a prerequisite for adopting the euro, in October 1990. The UK spent over £6 billion trying to keep its currency, the pound sterling, within the narrow limits prescribed by ERM, but was forced to exit the programme within two years after the pound sterling came under major pressure from currency speculators. The ensuing crash of 16 September 1992 was subsequently dubbed "Black Wednesday". During the negotiations of the Maastricht Treaty of 1992 the UK secured an opt-out from adopting the euro.

The government of former Prime Minister Tony Blair declared that "five economic tests" must be passed before the government could recommend the UK joining the euro and promised to hold a referendum on membership if those five economic tests were met. The UK would also have to meet the EU's economic convergence criteria (Maastricht criteria), before being allowed to adopt the euro. Currently, the UK's annual government deficit to the GDP is above the defined threshold. The government committed itself to a triple-approval procedure before joining the eurozone, involving approval by the Cabinet, Parliament, and the electorate in a referendum.

Gordon Brown, Blair's successor, ruled out membership in 2007, saying that the decision not to join had been right for Britain and for Europe. In December 2008, José Barroso, the President of the European Commission, told French radio that some British politicians were considering the move because of the effects of the global credit crisis. The office of the Prime Minister, Gordon Brown, denied that there was any change in official policy. In February 2009, Monetary Policy Affairs Commissioner Joaquín Almunia said "The chance that the British pound sterling will join: high."

In the UK general election 2010, the Liberal Democrats increased their share of the vote, but lost seats. One of their aims was to see the UK rejoining ERM II and eventually joining the euro, but when a coalition was formed between the Liberal Democrats and the Conservatives, the Liberal Democrats agreed that the UK would not join the euro during this term of government.

The United Kingdom, an EU member state, has not replaced its currency, the pound sterling with the common euro currency. The pound sterling does not participate in the European Exchange Rate Mechanism, a prerequisite for euro adoption. The UK negotiated an opt-out from the part of the Maastricht Treaty of 1992 that would have required it to adopt the common currency, and the Conservative-Liberal Democrat coalition government that was elected in May 2010 pledged not to adopt the euro as its currency for the lifetime of the parliament. Polls have shown that the majority of British people are against adopting the euro. In a June 2016 referendum the UK voted to withdraw from the EU, which if enacted would end any lingering discussion of it adopting the euro.