Donald Trump’s tariffs could inadvertently explode EU-UK tensions because of a little-known clause in the Brexit treaty that could harm Northern Ireland. Thanks to the 2023 Windsor Framework signed between former prime minister Rishi Sunak and EU Commission president Ursula von der Leyen, any retaliatory tariffs imposed by Brussels on the US would also be applied in Northern Ireland.

The US president announced he would slap the bloc with 20% tariffs on all goods sold to the US – twice as high as those being imposed on Britain. This was initially championed as a Brexit win, but the Windsor Framework clause could make it a bittersweet moment.

The EU has sounded much more bullish about retaliatory tariffs than the UK Government, which could mean Northern Ireland being carved off from Great Britain yet again.

DUP MP Gavin Robinson warned that Northern Irish businesses “must not become collateral damage” in any trade war between Brussels and Washington.

He told the BBC: “For those businesses, particularly in Northern Ireland who are drawing product from the EU, where they’re buying their product from is going to be impacted by tariffs.”

Former Brexit negotiator Lord Frost has now intervened to demand that, should this come into force, the UK Government must unilaterally disapply the Windsor Framework to ensure Northern Ireland is not hit.

He said: “If this comes to pass, then the Government should use Article 16 of the Protocol, on safeguards and trade distortion.”

He cited the relevant provision within the treaty: ”If the application of this Protocol leads to serious economic, societal or environmental difficulties that are liable to persist, or to diversion of trade, the Union or the United Kingdom may unilaterally take appropriate safeguard measures."

While this could save Britons in Northern Ireland from suffering higher costs, it would mean yet another furious showdown between London and the EU.

Stephen Kelly, head of campaign group Manufacturing NI, says: “If the UK does not reciprocate or do the same thing as the EU we are at a disadvantage.

“Companies that buy materials in Belfast from the US will pay more than their counterparts in Bolton.”

Meanwhile, former EU commissioner Mairead McGuinness questioned whether the White House had considered this major problem when setting the UK and EU’s tariffs rates.

She said: “I’m questioning and wondering if this is well thought-through from the US side? The US has always been a friend of the island of Ireland, and peace on this Ireland and stability.

“It certainly causes some difficulties. And rather than jump to a conclusion, I think we will have to look at this very carefully … this was not part of the discussions and thought processes when the Windsor framework was being negotiated.

“I mean, 10% isn’t good for Northern Ireland either. 20% isn’t good for us. Divisions like this aren’t helpful.”