Ten years on from the referendum, Ireland shows why Britain should join the EU single market again.

When the UK voted to leave the European Union in June 2016, no part of the UK had more at stake than Northern Ireland.

The frameworks that followed, from the Northern Ireland Protocol to the Windsor Framework of 2023, have provided some of the answers. But they have also created new complications, and the economic data now tells a story that should be at the heart of the UK's conversation about its relationship with Europe.

What the numbers reveal about Northern Ireland

Northern Ireland's trading relationship with the Republic has grown much stronger, while its trade with Britain has declined in relative importance. That is not a coincidence. It is the direct consequence of the Irish Sea border created by Brexit.

Cross-border trade in goods was broadly flat from 2000 to 2016, but since then there has been over a threefold increase in its value, reaching €10.6 billion / £9 billion in 2024 (FactCheckNI). Much of that growth reflects Northern Ireland firms reorientating towards the Republic because of Brexit-related red-tape with Britain.

But Northern Ireland has paid a price for this reorientation. Research shows that all other things being equal, increasing trade barriers and red-tape with Britain could cause Northern Ireland's GDP to contract by up to 2.6% (Citp).

The promise of "dual market access" to both EU and UK markets has also proved harder to realise than originally hoped. The Chief Executive of Invest NI told a committee at Stormont in October 2024 that there was no evidence of increased foreign direct investment as a result of Northern Ireland's unique dual market access status (Chartered Institute of Export & International Trade). The EY Economic Eye report forecasts growth of 1.3% for Northern Ireland in 2025 and 1.2% in 2026, compared with GDP growth for the Republic of Ireland forecast at 9% in 2025 (EY).

A different story in the Republic

The impact of Brexit on the Republic of Ireland has not been as profound as once feared, but that is not the same as saying Ireland came through it unscathed, or that anyone in Dublin regards it as anything other than a significant loss.

The Republic was always uniquely exposed. Approximately 15% of Irish goods and services exports are destined for the UK, and in the agri-food sector, around 40% of exports go to the UK market (Copenhagen Economics). Ireland was also, for decades, deeply integrated into British supply chains, with major retailers serving Irish outlets from distribution centres in northern England. Brexit dismantled much of that overnight.

The diplomatic damage was just as real. For years, Ireland and the UK had sat around the same table in Brussels, two close neighbours with overlapping interests and a shared stake in the peace process in Northern Ireland. Brexit did not just create a new border for goods. It removed the UK from the room where EU decisions are made, and with it, an ally Ireland had long relied upon. Relations between the two countries have been on a sustained upswing since Starmer took office, and the annual leaders' summit, inaugurated last year in Liverpool, is a symbol of that improvement (The Irish Times). But the very fact that such a summit needs to exist is a reminder of how much ground was lost in the years before because of Brexit.

That reset is continuing today. The second UK-Ireland Summit took place in Cork on Friday 13th March, with Prime Minister Starmer unveiling over £937 million in new Irish investment into the UK, alongside a new defence agreement and progress on energy interconnectors between the two countries (GOV.UK).

Where Ireland has seen some benefit, it has come largely through the hard work of Irish and EU officials, not through any particular good fortune. Ireland was allocated approximately €1 billion from the EU's Brexit Adjustment Reserve, the largest single allocation to any member state, representing 20% of the entire fund (European Commission). Without that support, and without the EU's insistence on protecting the integrity of the Single Market and the Good Friday Agreement, the situation on the island of Ireland could have been considerably worse.

There is also the matter of FDI. Brexit left Ireland as the largest of only two remaining EU countries where English is an official language, the other being Malta. That has made Dublin a more attractive destination for international businesses needing a foothold inside the EU single market. After Brexit, many UK-based firms moved their headquarters or opened subsidiary offices in Ireland to facilitate ease of business with other EU countries. In 2024, IDA Ireland recorded 234 inward investment projects, including 69 from first-time investors, set to create more than 13,000 future jobs (Silicon Republic).

But it would be wrong to frame any of this as Ireland winning from Brexit. The consensus in Dublin is rather that Ireland had a lucky escape, and that the escape was hard fought. The EU shield held. The diplomatic effort was enormous. And the relationship with the UK, which matters so deeply to Ireland economically, culturally, and in terms of the peace process, took years to begin recovering. It is only now, under this government, starting to resemble what it once was.

Ireland demonstrates why the UK should join the EU single market

What the data from the island of Ireland shows, more clearly perhaps than anywhere else in the UK or Europe, is what the EU single market actually means in practice. It means supply chains that flow freely across a border. It means businesses that can plan with certainty. It means a trading relationship built on shared rules rather than bespoke workarounds.

Research published by CEPR found that firms located further from the Irish border, and therefore more exposed to the full economic consequences of Brexit, reduced their workforce by up to 15.7% relative to less exposed firms (CEPR). The border did not just divide an island. It drew a line between two economic realities.

That is why, when Prime Minister Keir Starmer speaks about aligning more closely with the EU single market, the island of Ireland is one of the most compelling arguments available to him. The economic case is not abstract. It is visible, measurable, and human. It is the farmer in County Armagh rerouting her supply chain. It is the Belfast manufacturer who finds it easier to sell to Dublin than to Birmingham. It is the Republic's pharmaceutical sector, thriving precisely because it retained the frictionless access to European markets that the UK chose to give up.

The impact of Brexit on the island of Ireland highlights what the EU single market is for. And it makes the case, more powerfully than almost any other example, for why Britain should not merely align with it, but rejoin it.

For more on European Movement UK's campaign to bring Britain back into the Single Market, read more here and sign our petition.