Britain's Prime Minister Boris Johnson arrives with his dog Dilyn at the Methodist Hall in central London to cast his vote in local elections on May 5, 2022. Polls opened across the UK in local and regional elections that could prove historic in Northern Ireland and heap further pressure on embattled Johnson. Photo: AFP

Prime Minister Boris Johnson on Wednesday downplayed the prospect of triggering a UK trade war with the EU by threatening to pull post-Brexit arrangements in Northern Ireland, despite European warnings that he risks breaching international law.

Johnson said London and Brussels must "fix" the so-called Northern Ireland Protocol which governs trade to and from the British province, but that both sides should keep a sense of proportion.

"We're talking about really, in the scheme of things, a very, very small part of the whole European economy," he told reporters during an unrelated visit to Sweden and Finland.

"Let me put it this way: I don't think there's any need for drama. This is something that just needs to be fixed."

Johnson's government has warned it is ready to take unilateral action "to stabilize the situation in Northern Ireland if solutions cannot be found" to key sticking points with the protocol.

Ministers have argued that it does not command cross-community support and that London needs to protect the 1998 Good Friday Agreement, which ended three decades of sectarian violence over British rule in Northern Ireland.

But the European Union has repeatedly ruled out renegotiating the terms of the deal.

The standoff comes as political tensions rise in Belfast after historic elections last week saw pro-Irish nationalists Sinn Fein become the biggest party for the first time and now bidding to lead a power-sharing executive.

However, the latest UK threats to overhaul the arrangements unilaterally have caused consternation in Brussels, Ireland's foreign minister Simon Coveney said as he met Northern Irish leaders.

AFP