The Government is facing a legal challenge over legislation designed to allow it to expedite the building of border control posts at Northern Ireland ports.

The judicial review challenge, brought by loyalist activist Jamie Bryson, asserts that the statutory instrument enabling the completion of infrastructure for agri-food checks is unlawful because it treats Northern Ireland as the entry point into the European Union.

His claim states that the Northern Ireland Protocol itself asserts that Northern Ireland is part of the customs territory of the United Kingdom.

Mr Bryson’s legal representatives have served a pre-action letter to the Department for Environment, Food and Rural Affairs (Defra) and are expected to push for an emergency hearing in the High Court in Belfast this week.

The protocol, which was agreed by the EU and UK as a way to keep the Irish land border free-flowing post-Brexit, has created a series of new customs and regulatory barriers between Northern Ireland and the rest of the UK.

Negotiations between London and Brussels to resolve issues with the operation of the protocol are continuing.

The devolved powersharing institutions at Stormont collapsed last year after the DUP withdrew co-operation as part of its protest against the protocol.

In the absence of devolved government, responsibility falls on Defra to construct new facilities at Northern Ireland ports to check goods entering Northern Ireland from the rest of the UK.

Last month, the government published legislation to ensure completion of the facilities for agri-food checks.

The pre-action letter, seen by PA news agency, states that Defra has “failed to consult on a matter of public significance and importance” given the impact of the legislation is to “treat Northern Ireland as the entry point into the European Union”.

It continues: “The purpose of the regulations, set out in the explanatory notes and various public statements by the Government, is to facilitate the construction of border control posts, internally within the United Kingdom.”

Mr Bryson said: “The relevant statutory instrument treats Northern Ireland as the entry point into the European Union territory.

“This is not only a constitutional absurdity, but it is even at variance with the protocol itself which at Article 4 proclaims Northern Ireland is part of the customs territory of the UK.

“This legal challenge will force the Government to confront the duplicity of their actions in claiming to be seeking to restore Northern Ireland to the UK, whilst at the same time, in fact laying regulations to treat Northern Ireland as part of the EU.”

Defra has been contacted for comment.