BritIn, BritOut, but slowly

The UK voted ten years ago on 23 June 2016 to leave the European Union. 

It then took 1,318 days for the UK to finally leave the EU due to tortuous negotiations and deliberations both between the EU and the UK as well as within the UK itself.

Those 1,318 days were almost nothing when compared with the 12 years of negotiations which preceded the UK joining the European Communities (now, the EU) in 1973.

And is a similar protracted process now going to start if the UK wants to rejoin the EU?

Andy Burnham – the seventh UK Prime Minister since the 2016 Brexit Referendum – has raised the prospect that the UK will certainly get closer to the EU and could even rejoin the 27 Member bloc. 

Even if Andy Burnham started the rejoining process, there is no guarantee that he would still be in office if it happens or, moreover, that the UK would rejoin the EU. 

Legally, what would BritIn – the UK rejoining the EU - look like? How would it happen?

There is no fast lane for rejoining Member States. The EU has never had to deal with a re-joiner, and the treaties are silent on the issue.  There is no legislation giving any preference for a re-joiner; one has to queue up in the usual way. 

In essence, article 49 of the Treaty on European Union comes into play. The article gives little away other than all the existing EU member states must agree unanimously to admit the new member state:

“Any European State which respects the values referred to in Article 2 and is committed to promoting them may apply to become a member of the Union. The European Parliament and national Parliaments shall be notified of this application. The applicant State shall address its application to the Council, which shall act unanimously after consulting the Commission and after receiving the consent of the European Parliament, which shall act by a majority of its component members. The conditions of eligibility agreed upon by the European Council shall be taken into account.

The conditions of admission and the adjustments to the Treaties on which the Union is founded, which such admission entails, shall be the subject of an agreement between the Member States and the applicant State. This agreement shall be submitted for ratification by all the contracting States in accordance with their respective constitutional requirements.”

There will be a natural reluctance by some Member States to let the UK return. Some Brexiteers may say that the UK will never rejoin but the practical reality is that some in the EU would equally be resistant to the UK rejoining. While others would want the UK to give certain guarantees. 

The UK could be obliged to commit to membership for a minimum period but that could cause difficulties later as the time period would be about to expire and tensions run high. Membership in the EU is meant to be forever, but Member States may leave – as demonstrated by the CJEU judgment in C-621/18 Wightman and Others.  Some in the EU would wonder whether renewed membership would survive a change of government so some commitment may be needed.

Some Member States could use their veto power to win other non-UK related battles within the EU itself - unanimity among EU Member States is required for admit a State. So, it is possible that accession could be difficult. For example, a Member State could block the UK’s re-entry to win a deal on another entirely unrelated issue.  So, UK’s re-entry could be delayed or even denied because of some other unrelated issue.

There is some media speculation that the UK would have to abandon the pound sterling and accept the euro as a condition of membership. This is not inevitable. Six EU Member States still do not use the euro. Denmark – an EU Member State for over half a century - even has an official and legally binding opt-out agreed in 1992. It is far from inevitable that the UK would have to give up the pound sterling, but it would certainly be encouraged to adopt the euro.

The key driver for the UK for renewed membership would probably be access to the “internal market”. This “internal market” comprises the free movement of goods, services, capital and people.  Many in the UK would be happy with the free movement of goods, services and capital but the four come as a package. The EU would be unwilling to accept a “Meatloaf Deal” where “two out of three ain’t bad” or, more accurately, “three out of four ain’t bad” – the UK would have to sign up for the whole package. One of the features of the Brexit debate in 2016 was how many people preferred goods over people.

The UK might go for a customs union deal (i.e. a deal on customs and a common external tariff) but not an internal market deal.  That would not suit the likes of Ireland and be somewhat difficult to operate.

It may even be that the EU could create a new mezzanine-level organisation – a sort of half-way house – and that could suit the likes of the UK and Ukraine. It would help placate opposition by some Brexiteers but may not be enough for others.

But how realistic is the UK rejoining? It is like remarrying the same person that you divorced. That has happened – the current Japanese Prime Minister, Sanae Takaichi, remarried her ex-husband Taku Yamamoto in 2021 whom she had divorced four years earlier.

But would countries re-join an organisation that they had left?  That too has happened. The US left UNESCO in 1984 and then rejoined in 2003 only to leave again in 2018. The US then re-rejoined in 2023 before announcing another withdrawal to take effect at the end of 2026. So, the US is scheduled to leave UNESCO at the end of 2026 for the third time.  The US also left the International Labour Organization in 1977 and rejoined in 1980. And even the UK has form: it left UNESCO in 1985 and rejoined in 1997. So, a State rejoining an international organisation is possible.

Would it need another referendum in the UK?  Legally, no but practically, yes. The UK joined in 1973 without a referendum beforehand but then it had a referendum in 1975 to decide whether to remain – Margaret Thatcher famously supported remaining.  A referendum would now be a political necessity as a vote of the people decided Brexit and hence it would, in practical terms, require a vote of the people. Anything short of a referendum would be unconvincing for many. The experience from Ireland re-running EU referendums is that something needs to change before people can be convinced to change their minds.

What are the lessons for a new referendum? The question put to the people must be clear-cut; the 2016 question was not clear and was probably biased towards leaving. It asked whether people wanted to “leave” but did not specify to where they were leaving so “leave” had multiple meanings and could therefore attract diverse voters. The electorate needs to know the issues fully and be given all the requisite information. There has got to be a full debate and full disclosure, but it could well be very fractious.  And the EU has to make membership attractive enough to swing marginal voters if the EU wants the UK to rejoin.

Would BritIn happen? Ireland would be probably the strongest supporter of the UK rejoining. Even if the UK wanted to rejoin, it is far from inevitable that the whole of the EU would agree to it rejoining.  Any Member State may veto the UK’s accession. Some would have seen the UK as always having been a semi-detached non-committed Member State so they may wonder about its desire to rejoin.  The EU has found it easier to reach consensus and agreement post-Brexit and some may not want any upset to that new balance. The UK may not be as attractive a partner for the EU as some Brexiteers thought – some of them argued that “Brexit could be sorted in an afternoon over a cup of coffee".

Could it happen? Yes, but there will be long and intensive negotiations. Trust would have to be built and demonstrated.

The second EU-UK summit on 20 November 2026 could see some developments but how long would the negotiations take? The answer to that is simple: years. 

There are no two ways of putting it, it would take years. The EU would negotiate it thoroughly and they would want to see that membership would survive a general election and regime changes in the UK. 

BritIn could happen but the longer it takes to start the re-entry process, the longer it will become.

For more information, please contact Dr Vincent Power.

Date published: 22 October 2026