The Supreme Court determined whether the clause ousted the supervisory jurisdiction of the High Court to quash a judgment for error of law. It also resolved whether Parliament can oust the said jurisdiction, and if it can, what principles will apply.

“The legal issue decided by the IPT is not only one of general public importance, but also has possible implications for legal rights and remedies going beyond the scope of the IPT’s remit,” Supreme Court Judge Robert Carnwath, Lord Carnwath of Notting Hill, said in the lead judgment. “Consistent application of the rule of law requires such an issue to be susceptible in appropriate cases to review by ordinary courts.”

The ruling comes after a five-year battle spearheaded by advocacy group Privacy International. It said that the judgment is a “major endorsement and affirmation of the rule of law in the UK” and that it “guarantees that when the IPT gets the law wrong, its mistakes can be corrected.

“Today's judgment is a historic victory for the rule of law,” said Caroline Wilson Palow, Privacy International general counsel. “Countries around the world are currently grappling with serious questions regarding what power should reside in each branch of government. Today's ruling is a welcome precedent for all of those countries, striking a reasonable balance between executive, legislative and judicial power.”

She also said that the judgment helps the group’s challenge to the UK government's use of bulk computer hacking warrants.