What is the Irish backstop?

Published: 8th Aug 2019

The “Irish backstop” is effectively an insurance policy in UK-EU Brexit negotiations. It’s meant to make sure that the Irish border remains open (as it is today) whatever the outcome of the UK and the EU’s negotiations about their future relationship after Brexit.

The backstop is part of the draft withdrawal agreement negotiated between Theresa May’s government and the EU.

Under the draft withdrawal agreement, the UK would enter a “transition period” after Brexit (currently timetabled to be 31 October 2019).

During this period (which would last until, at the latest, December 2022) we’d still be in the single market and customs union, and continue to trade with the EU as we do now.

The plan was for the government to negotiate our future relationship with the EU, including trade rules, during this transition period.

The “Irish backstop” would kick in at the end of the transition period if the UK and EU had failed to negotiate a future trade deal that kept the Irish border open as it is today.

Under the backstop the whole of the UK would enter a “single customs territory” with the EU. There are many parts to this but essentially there would be no tariffs on trade in goods between the UK and the EU and some (though not all) trade restrictions would be removed.

However, Northern Ireland alone would remain aligned to some extra EU rules to ensure the Irish border remains open as it is today. These separate regulations for Northern Ireland would mean there would be some checks on goods entering Northern Ireland from the rest of the UK.

The Irish backstop has been highly controversial among some MPs, and is one of the main reasons why the withdrawal agreement has so far failed to pass through parliament. The new Prime Minister, Boris Johnson, now claims the backstop is “dead”. The rest of this piece explains how the political situation around the backstop has evolved over time and why the Irish border is an important topic.

  1. Recent updates
  2. Why is there a backstop specifically for the Irish border?
  3. Why could Brexit affect the border?

Recent updates

Since this article was originally published in October 2018, the political situation around the backstop has changed. This is a summary of the main developments:

The terms of the backstop were finalised in November 2018.

Many MPs criticised the backstop for two main reasons. That it would lead to different regulations for Northern Ireland compared with the rest of the UK (which some thought threatened the integrity of the UK), and that the UK would not be able to leave the backstop without EU approval.

The withdrawal agreement says that the UK and the EU could get rid of the backstop requirements, but only if both the UK and the EU agree it's not necessary to avoid a hard border in Ireland.

In other words, the UK couldn’t opt out of the Irish backstop if the EU felt that any alternative solution wouldn’t work.

The EU and UK both said they didn’t want the backstop to be used but this wasn’t enough assurance for some MPs who felt that the backstop could mean the UK remaining closely aligned to the EU indefinitely.

Parliament voted against the withdrawal agreement in January 2019, for the first time.

In March 2019, the UK government and the EU agreed an additional “instrument” on the backstop, intended to address these concerns.

In the opinion of the Attorney General (the government’s chief legal advisor), this instrument reduced the likelihood that the UK would be kept in the backstop against its will if the EU was blocking negotiations over the future relationship arrangements in bad faith.

However the legal advice also said that, if no bad faith on the EU’s part could be proven, the instrument didn’t reduce the likelihood that the UK could be kept in the backstop.

In practice this meant the UK could not unilaterally leave the backstop in a scenario where an impasse had been reached between the UK and the EU, not through any demonstrable failure by either party, but simply because of “intractable differences.”

The withdrawal agreement, plus the new “instrument” on the backstop, were rejected by parliament in March 2019. The withdrawal agreement was rejected for a third time later that month.

The new prime minster, Boris Johnson, last week declared both the backstop and withdrawal agreement to be “dead”.

He seems set to try to avoid the backstop through different means—either by trying renegotiate the deal with the EU, or by leaving the EU with no deal.

It seems unlikely that the EU would sign up to any withdrawal agreement that doesn’t include the Irish backstop or something very similar.

Why is there a backstop specifically for the Irish border?

The Irish border was singled out by both the UK and the EU for a backstop because of its importance for the Northern Irish peace process. The 1998 Good Friday Agreement was a key part of this peace process. One of the agreement’s three main points was creating the infrastructure for “North-South co-operation” between the Irish government and the newly-created Northern Irish Assembly.

This cross-border cooperation was a part of a strategy of “‘normalisation’ of relations between Protestant and Catholic communities within Northern Ireland and across the border”, according to the Institute for Government.

A key part of this ‘normalisation’ and cooperation process was the opening up of the border, which had previously been manned by British soldiers. Today, there are no checks at all on people or goods as they move either way between Northern Ireland and the Republic of Ireland, and trade across the border was worth £4 billion in 2016. The Irish government has said that the open border is “the most tangible symbol of the Peace Process”.

Both the UK and EU agreed that, in negotiating a deal on the relationship after Brexit, keeping the border open and upholding the terms of the Good Friday Agreement was of critical importance. That’s why they committed to the principle that, even if future trade negotiations fail, there should be provisions in place to ensure that the border remains open, as it is today. That principle is the Irish backstop.

Why could Brexit affect the border?

The creation of an open border was, at least in part, made easier by the UK and Ireland both being EU members, and therefore part of the customs union and single market, which allows (among other things) the free movement of goods and people between EU countries.

As part of Brexit, the UK intends to leave both the single market and customs union. The terms of the Good Friday Agreement can be upheld without the UK being part of these two things, although customs and regulatory checks on goods will be necessary in some form (possibly away from the border).

Were the UK to leave the EU with “no deal” (in the event that the draft withdrawal agreement doesn’t get approved by parliament), Northern Ireland (as part of the UK) would have different customs and regulatory standards to Ireland (as part of the EU). This means there could be a need for customs checks on goods to be introduced at the border, which could create a “hard border” with physical infrastructure, like cameras or guard posts. This would undermine the principle of North-South cooperation as set out in the Good Friday agreement.

In March, the UK government set out its plan for avoiding a hard border in Ireland in the case of no deal. It says it would introduce no new tariffs on goods crossing the border from Ireland into Northern Ireland, and no new checks or controls at the border itself (although some new customs requirements would be placed on a small number of goods, these would happen away from the border.

This is a unilateral measure set out by the UK government, meaning it only affects goods crossing from Ireland into Northern Ireland. 

As for goods going the other way (from Northern Ireland into Ireland) Pierre Moscovici, the EU’s Commissioner for Economic and Financial Affairs, Taxation and Customs, said there would be border checks, but “in the least disruptive manner possible and as much as possible away from the border”. The exact details of how this would be done remain unclear.

The government also emphasises that these measures would be temporary, and that it would continue to seek a permanent, negotiated solution to Irish border situation.

The government confirmed to us that, following the change of prime minister in July, this guidance still applies.

Correction 9 January 2019

A previous version of this piece incorrectly stated critics of the Irish backstop have concerns "it will lead to different regulations for Northern Ireland compared with the rest of the EU", this should have read "rest of the UK".

Update 15 March 2019

This piece has been updated following parliamentary votes in the week of 11 March.

Update 8 August 2019

This piece has been updated to cover the latest political developments around the backstop.


We aim for our factchecks to be as accurate and up-to-date as possible. If you think we've made an error or missed some relevant information, please email team@fullfact.org.