Would we have to join the euro?

The UK had an opt-out from the euro currency during its membership of the EU. If we rejoin, would we finally be made to adopt it?

This one is a favourite of Brexiters because adding a requirement for euro membership noticeably reduces the support for rejoining the EU in polling. For example, in one 2024 poll that showed headline support for rejoin at 57%, asking about rejoin “if Britain had to adopt the euro as a condition of rejoining” saw support fall to 46%.

However, while EU membership creates a theoretical obligation to adopt the euro, it has not been that clear-cut in practice.

Not all EU countries use the euro

The EU’s official line, that all member states are required to adopt the euro unless they have an opt-out, is technically true as a legal position, but not enforced as a matter of politics.

Currently, 20 EU countries use the euro and 7 do not (see table, next page). Only one of these states, Denmark, has an actual opt-out.

There is no process for the EU to force states to join the euro, or to sanction states that refuse

States that do not wish to adopt the euro, most notably Sweden, are still technically obliged to do so if they ever meet the criteria – but they can simply ensure that they never meet them. On the flip side of this, some states such as Bulgaria are actively trying to join the euro, but at the time of writing are yet to meet all of the criteria.

There is no process for the EU to force states to join the euro, or to sanction states that refuse. Jean Claude Juncker, then the president of the European Commission, said in 2017: “I have no intention of forcing countries to join the euro if they are not willing or not able to do so.” The European Commission reiterated in 2022 that “no timetable is prescribed”. In other words, joining the euro can be delayed indefinitely, meaning in reality that it can be avoided.

Euro adoption is a stringent process (see below), and not one that could happen accidentally or, importantly, without the consent of the country concerned.

The seven EU countries without the euro

These seven countries have been members of the EU for a combined 174 years without being made to join the euro. Bulgaria does hope to join soon, at its own request.

Denmark has an opt-out from the euro, but Sweden does not, and no action has ever been taken against Sweden over the issue.

A political question

The subtleties of this position lead to a few political problems in practice.

Firstly, would the EU accept a new member that makes clear in advance its intentions to indefinitely ‘delay’ euro membership in this way?

Secondly, would the British population understand and accept the position above, or would Brexiters simply be able to shout about the headline ‘obligation’ to join the euro in order to hurt the popularity of rejoining?

The answers to these questions cannot yet be known. Ultimately this is where the issue would need to be resolved politically – just as the above quoted statements about having “no intention of forcing countries to join the euro” were issued in response to a particular moment of political pressure. The EU could offer similar reassurances again in future, especially if it knew that a UK referendum was coming where the euro would become an issue. Alternatively, it could offer some firmer recognition of the current de facto position that some EU countries do not intend to join the euro.

This is not just part of the discussion about the UK rejoining but part of a wider debate, as the EU has already begun to talk about how to handle the issue of the euro ahead of Ukraine and the Balkan countries joining in the next planned round of EU enlargement.

For reference: Euro convergence criteria

In 2018, the last time the criteria were calculated while the UK was an EU member, the UK (if it did not have an opt-out) would have failed to meet them because of high inflation, a high debt-to-GDP ratio and the lack of ERM II membership. In other words, the UK could not have joined the euro even if it wanted to.

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