The Supreme Court will later rule on the lawfulness of Brexit’s Northern Ireland Protocol.
The legality of the contentious trading arrangements has been challenged by a collective of unionists and Brexiteers.
Arguments were considered by the UK’s highest court at a two-day hearing last year after the Court of Appeal upheld a ruling in Belfast High Court dismissing the legal challenge.
The protocol, which is a key aspect of the Brexit Withdrawal Agreement, was jointly designed by London and Brussels to keep Ireland’s land border free flowing following the UK’s departure from the EU.
Becoming effective in 2021, the arrangements instead shifted customs and regulatory checks to the Irish Sea and created new red tape on the movement of goods between Great Britain and Northern Ireland, with trade in the region remaining subject to certain EU Single Market rules.
The appellants argue that the legislation passed at Westminster to give effect to the Withdrawal Agreement conflicts with the 1800 Acts of Union that formed the United Kingdom, particularly Article 6 of that statute guaranteeing unfettered trade within the UK.
The legal challenge also contends that the protocol undermines the peace process legislation underpinning Northern Ireland’s powersharing settlement at Stormont – the 1998 Northern Ireland Act.
The Northern Ireland Act, which gave effect to the historic Good Friday peace agreement, guarantees that the constitutional status of the region can only be changed with the consent of its citizens via referendum.
It also includes cross community provisions (Section 42) that ensure controversial decisions at Stormont can only be taken if they are supported by a certain proportion of both nationalist and unionist MLAs.
The Withdrawal Agreement does provide for a future Assembly vote on the continuation of the protocol, however the UK Government has amended Stormont rules so the vote can be passed on a straight majority basis, rather than having to meet the cross community consent thresholds.
In 2021, Belfast High Court judge Mr Justice Colton dismissed a judicial review challenge against the lawfulness of the protocol on all grounds.
His judgment was upheld by the Court of Appeal last year.
While the Appeal Court found that the protocol does conflict with the Acts of Union in respect of unfettered trade, judges ruled that the 1800 statute had been lawfully modified by Parliament.
The court also dismissed the argument that the post-Brexit trading arrangements have changed the constitutional status of Northern Ireland.
It further ruled that the Government did have the authority to disapply the cross community voting provisions in the Stormont Assembly when it came to the vote on the future of the protocol.
The Court of Appeal later granted leave for the case to be referred to the Supreme Court.
The case involves two conjoined challenges – one taken by unionist politicians and Brexiteers including Traditional Unionist Voice (TUV) leader Jim Allister, former Brexit Party MEP Ben Habib and Baroness Kate Hoey and the other mounted by a loyalist pastor from Belfast, Clifford Peeples.