A judge at Belfast High Court has rejected all grounds of two joined legal challenges that argued the terms of Brexit's Northern Ireland protocol were unlawful.
Judicial review proceedings had been launched against the protocol in the name of unionists from across the UK, including former DUP leader Arlene Foster, former UUP leader Steve Aiken, TUV leader Jim Allister, former UUP leader Lord Trimble, former Brexit Party MEP Ben Habib and Baroness Hoey.
Mr Justice Colton today rejected claims that the Protocol breaches both the Acts of Union 1800 and the 1998 Good Friday Agreement.
He also declared: "The making of treaties and the conduct of foreign affairs are matters of high level politics which are entirely unsuited to supervision by a court on a judicial review application."
The ruling represents a setback for the pan-unionist coalition staunchly opposed to the protocol due to the constitutional damage they believe it has caused to Northern Ireland's position within the UK.
They are now expected to mount an appeal.
Implemented as part of the Brexit Withdrawal Act, the protocol created a trade border in the Irish Sea between Britain and Northern Ireland.
With the north remaining in the EU single market for goods, it has led to disruption to business at Irish Sea ports since January.
Counsel for the unionist coalition, former attorney general John Larkin QC, claimed the protocol is incompatible with domestic and European law.
He argued that it had been "inflicted" on the north in breach of enshrined rights to representative democracy.
During submissions, Mr Larkin branded the trading agreement between the UK and EU "legally rotten to the core".
It was contended that the protocol breaches Article 6 of the Act of Union by leaving Northern
Ireland inside the EU's customs union.
Tony McGleenan QC, representing the British government, countered that Parliament had full legal authority to implement the terms.
Part of the case centred on the concept of implied repeal, where a later Act is assumed to take precedence over earlier conflicting legislation.
Delivering judgment, Mr Justice Colton held that the 2018 Withdrawal Act overrides Article 6 of the Act of Union.
"The more general words of the Act of Union 1800 written 200 plus years ago in an entirely different economic and political era could not override the clear specific will of Parliament, as expressed through the Withdrawal Agreement and Protocol, in the context of the modern constitutional arrangements for Northern Ireland," he said.
"This matter must also be considered in light of the fact that every provision and clause of the Withdrawal Acts, the Protocol and associated documents were fully considered by Parliament."
He also concluded that the Northern Ireland Act 1998, which brought the Good Friday Agreement into law, has no impact on the legality of the changes brought in by the Protocol.
A further ground of challenge centred on an alleged infringement on the right to free elections within Article 3, Protocol 1 (A3P1) of the European Convention of Human Rights.
With Northern Ireland's citizens said to be subject to laws over which they have no say in, Mr Larkin branded the legislative changes "constitutional vandalism".
At one stage the north was likened to a colony, or the Vichy government in France under the Nazi regime during the Second World War.
Mr Justice Colton described those comparisons as wide of the mark and unhelpful.
"Whatever be the criticisms of the Protocol they are not apt for comparison with a World War which resulted in millions of deaths and widespread economic devastation," he said.
The judge added: "It is important to recognise that the Withdrawal Agreement including the Protocol has been thoroughly considered by the UK Parliament and has been enacted by way of primary legislation and regulations made under that primary legislation.
"The legislature was implementing the result of a referendum; the government was implementing a policy for which it obtained a mandate from the electorate in the UK and... ensured that Parliament approved any agreement it entered into with the EU.
"There has been a thorough review of the Protocol by Parliament."
It was stressed that Northern Ireland remains a part of the UK, electing members directly to the UK legislature which ratified the Withdrawal Agreement and can, if it desires, amend or repeal the associated Acts.
"In light of the democratic protections provided in the Protocol the means adopted by the UK are not disproportionate," Mr Justice Colton held.
"Residents in Northern Ireland have the right to vote for two legislatures, namely the Northern Ireland Assembly - of which three of the applicants are currently members - and the UK Parliament, who between them have the ongoing ability to influence, consent to or bring an end to existing and future EU laws arising from the safeguards and protections that have been built into
the Protocol.
"In this way the A3P1 rights of residents in Northern Ireland have been protected."
Part of the challenge was directed at alleged breaches of Article 10 of the Treaty on European Union (TEU), which sets out how its functions are founded on representative democracy.
However, the judge concluded that the principle of Parliamentary sovereignty ultimately defeated claims of a violation of EU law.
He stated: "The court should not interfere with or ignore the clearly expressed will of Parliament in passing primary legislation to implement a valid agreement between contracting parties, both of which endorsed that Agreement through their respective constitutional orders."
A related case taken by loyalist pastor Clifford Peeples was also rejected.
The Belfast man's lawyers claimed the protocol breaches the Good Friday Agreement and must be subject to a referendum.
But Mr Justice Colton determined: "The protocol is the outworking of the political compromises designed to preserve and protect the Belfast/Good Friday Agreement."
Outside court, Mr Allister confirmed the ruling would be appealed, with a case potentially set for the Supreme Court.
"This battle is far from over because we refuse to accept that the Union is over, which is the message of the Protocol," he said outside Belfast High Court.
Baroness Hoey added: "We are committed to carrying this on because I think today's judgment really has shown that the people of Northern Ireland need to wake up to the fact that the Union now has been broken and that we are going to have to fight back.
"So can I thank everybody in Northern Ireland who has given us support and make it absolutely clear that this is only the beginning of the legal challenge and also of people's protests against what has been done to us without our consent."
Mr Habib said British prime minister Boris Johnson had to act.
"The judge found against us on every ground but, crucially, what he found was the Act of Union Article 6, a fundamental part of the Act of Union 1800, no longer exists, that Northern Ireland and Great Britain have effectively been severed by the Protocol," he said.
"It seems to have just gone through Parliament without even the prime minister recognising that his own act, the Northern Ireland Protocol, has actually broken the union of the United Kingdom.
"He denied it in the Commons the other day but actually that's precisely what this High Court has just ruled, the union of the United Kingdom has been broken."
He added: "The only positive that you might put on it (the court ruling) is we do now officially know that the union of the United Kingdom has been trampled on by the Protocol, that the union has been broken.
"At least that now is out in the open, that's out in the open.
"The prime minister has to face up to the reality that his own judicial system has said that the union of the United Kingdom has been broken and he has to grapple with it, he needs to put that right."
