The leader of the Democratic Unionist party, Arlene Foster, and senior DUP MPs are launching a legal action challenging the Brexit deal’s Northern Ireland protocol. They will be joining other unionists from across the UK in judicial review proceedings unless alternative post-Brexit trade arrangements are put in place that secure their consent. The DUP deputy leader, Nigel Dodds, the party’s Westminster leader, Sir Jeffrey Donaldson, and its chief whip, Sammy Wilson, are backing Foster’s action in response to disruption of business through Irish Sea ports. A separate group of DUP members have engaged senior legal counsel to prepare for a series of challenges to the protocol. Foster said: “Fundamental to the Act of Union is unfettered trade throughout the UK. At the core of the Belfast agreement was the principle of consent, yet the Northern Ireland protocol has driven a coach and horses through both the Act of Union and the Belfast agreement.” Unionists and loyalists have been growing increasingly angry at new regulatory and customs processes required to bring goods into Northern Ireland from the rest of the UK. Nationalists and the Irish government are committed to solving problems with the protocol keeping Northern Ireland within the EU’s single market but insist nothing must threaten the free flow of commerce on the island of Ireland. The nationalist SDLP leader and Foyle MP Colum Eastwood said: “The DUP’s legal action against the Ireland protocol is ill judged and will only further entrench the febrile political environment as well as creating further uncertainty for people and businesses. “There will be few with sympathy for the argument that the protocol, which prevents a hard border in Ireland and guarantees dual market access for local businesses, breaches the Good Friday agreement.” The DUP group has sought the legal opinion of constitutional law experts before several potential high court challenges in Belfast and London against the government over the post-Brexit Irish Sea trading arrangements. A party source involved in the initiative told PA that preparatory work on a “series of very significant legal challenges” was at an advanced stage. “No stone will be left unturned in the pursuit of justice for the people of the union,” the source said. They are also joining a legal challenge by the former Labour MP Kate Hoey, the Traditional Unionist Voice leader Jim Allister and the former Brexit party MEP Ben Habib. Unionists have argued that the protocol undermines the Act of Union and the Northern Ireland Act, which gives legislative effect to the 1998 Good Friday/Belfast agreement, which established devolved powersharing. The DUP leadership has presented a five-point plan in recent weeks aimed at frustrating the operation of the protocol. That campaign includes a boycott of north-south ministerial engagement on issues related to the contentious trading arrangements. The party also started an online petition to secure a parliamentary debate on the protocol. The debate is due to take place at Westminster on Monday. The protocol was agreed by the EU and UK to overcome one of the main sticking points in the Brexit withdrawal talks, regarding the Irish border. It keeps that frontier free-flowing by Northern Ireland remaining in the single market for goods and applying EU customs rules at its ports. The protocol instead moved the regulatory and customs border to the Irish Sea, with a series of checks, certifications, inspections and declarations now required on many goods being shipped into the region from Great Britain. This has led to some trading disruption since the end of the Brexit transition period on 31 December.