The Protocol is the name given to the trade agreement in place for Northern Ireland in the aftermath of Brexit. Frequently derided by DUP members like party leader Jeffrey Donaldson, the Supreme Court’s decision means the Protocol is in line with the law.
Speaking after the ruling, Donaldson said: "A solution to the protocol was never going to be found in the courts, but the cases have served to highlight some of the reasons why unionists have uniformly rejected the protocol.
"The Government must consider this judgment, their own arguments to the court and take the steps necessary to replace the protocol with arrangements that unionists can support. The protocol represents an existential threat to the future of Northern Ireland's place within the Union. The longer the protocol remains, the more it will harm the Union itself.
"The checks on the Irish Sea border are the symptom of the underlying problem, namely, that Northern Ireland is subject to a different set of laws imposed upon us by a foreign entity without any say or vote by any elected representative of the people of Northern Ireland.
"Over eighteen months ago we outlined the parameters for the way forward. We set our tests and those continue to be our yardstick for measuring any deal between the EU and UK.
"Political progress in Northern Ireland was hard won and is built on the support of unionists and nationalists. Not one unionist MLA or MP supports the protocol. The idea that one section of our people will dominate the other and ignore the concerns of unionists is the opposite of powersharing and will never produce durable or balanced outcomes.
"There will be no solid basis for an executive and assembly until the protocol is replaced with arrangements that restore NI's place in the UK internal market and our constitutional arrangements are respected."