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The system through which U.K. spy agency GCHQ can access data from NSA mass surveillance programs was in violation of fundamental rights, the Investigatory Powers Tribunal has ruled. However, the limits of that finding have left human rights groups dissatisfied.

The decision came as a result of a case brought about by Privacy International, Liberty and other human rights groups regarding the Prism and Upstream programs. Prism is the scheme through which U.S. intelligence gets users’ communications from service providers in that country, and Upstream intercepts bulk data from the internet’s core infrastructure.

In December the IPT ruled that it was legal in principle for GCHQ get data from these programs now – i.e. from December 2014, in the post-Snowden world, where people actually know what’s going on — but it held back on saying whether there had been historical breaches of human rights.

Having subsequently heard out both the complainants and the intelligence agencies, the tribunal said on Friday that the data-sharing regime had violated the rights to privacy and free expression, as set out in Articles 8 and 10 of the European Convention on Human Rights. However, it reiterated that it believes the system now no longer does so.

In a statement on Friday, Privacy International said it and Pakistani NGO Bytes For All would ask the IPT, which generally acts as a secret court, to “confirm whether their communications had been unlawfully collected prior to December 2014 and, if so, demand their immediate deletion.”

The groups also disputed the December ruling’s assertion that the disclosure of “a limited subset of rules governing intelligence-sharing and mass surveillance” made everything OK. They will now appeal that ruling with the European Court of Human Rights, as will Liberty.

Here’s what Liberty legal director James Welch said in the statement:

We now know that, by keeping the public in the dark about their secret dealings with the National Security Agency, GCHQ acted unlawfully and violated our rights. That their activities are now deemed lawful is thanks only to the degree of disclosure Liberty and the other claimants were able to force from our secrecy-obsessed Government. But the Intelligence Services retain a largely unfettered power to rifle through millions of people’s private communications – and the Tribunal believes the limited safeguards revealed during last year’s legal proceedings are an adequate protection of our privacy. We disagree, and will be taking our fight to the European Court of Human Rights.

“We must not allow agencies to continue justifying mass surveillance programs using secret interpretations of secret laws,” Privacy International deputy director Eric King added. “The world owes Edward Snowden a great debt for blowing the whistle, and today’s decision is a vindication of his actions.”