Top government officials in Scotland are under pressure to explain their knowledge of a secretive police surveillance unit that was exposed in documents leaked by National Security Agency whistleblower Edward Snowden.

On Tuesday, cabinet secretary for justice Michael Matheson was grilled in the country’s parliament about the so-called Scottish Recording Centre and its previously undisclosed involvement in covert surveillance operations.

As The Intercept revealed last week, the Recording Centre is one of several domestic organizations within the United Kingdom involved in a top-secret program named MILKWHITE, which has provided law enforcement agencies with access to “bulk” internet data intercepted by the British eavesdropping agency Government Communications Headquarters, or GCHQ. Prior to the disclosure, few in Scotland knew the Recording Centre even existed — much less that it has been tapping into GCHQ’s troves of data.

In recent days, several Scottish media outlets have picked up the issue, increasing pressure on the government. Questioned about the revelations on Tuesday, Matheson told the Scottish parliament that the government “takes the protection of our citizens’ civil liberties extremely seriously and we are clear that investigatory powers should only be used when it is necessary and proportionate to do so. But we must always balance those fundamental civil liberties with the need to ensure our law enforcement bodies have effective powers to investigate and deal with serious organized crime.”

He declined to comment on any relationship with GCHQ and stated that police must obtain a warrant signed off by a government minister to intercept communications. However, documents about the MILKWHITE program show that it stores metadata about emails, instant messenger chats, and social media activity, meaning it contains information that could reveal the sender and recipient of an email or message, but not the written content. And police agencies in the U.K. do not require a warrant to access this kind of information. They only require a warrant when they want to monitor the content of a communication — for instance, the audio of a call or the body of an email.

Matheson’s response, perhaps unsurprisingly, did not satisfy opposition politicians. John Finnie, a member of the Scottish parliament representing the Green party, said in a statement: “The Cabinet Secretary today attempted to give the impression that all policing activities in Scotland are proportional and that interceptions are independently approved but as we know that is not always the case. There is clearly a culture of bulk collection of data that needs [to be] reined in. I will continue to challenge such over-reaching activities.”

The revelation about the Recording Centre, the first from the Snowden archive to implicate Scotland’s authorities, has put the ruling Scottish National Party in an awkward spot.

Just last week, the party’s leadership took a strong stand against the U.K. government’s push to obtain more surveillance powers through the controversial Investigatory Powers Bill, dubbed the “Snoopers’ Charter” by critics. Joanna Cherry, the Scottish National Party’s spokesperson on justice and home affairs, had raised concerns about the proposed new powers for “bulk” surveillance, which she blasted as “extremely intrusive.”

However, the Snowden documents about MILKWHITE indicate that Scotland’s police forces — through the Recording Centre — have been accessing bulk data for years, presumably with sanction from top Scottish government ministers.

Alistair Carmichael, a Liberal Democrat member of parliament, was quick to point out this inconsistency — and has pledged to take up the issues surrounding the Recording Centre and the MILKWHITE program with the British government’s Home Office in an attempt to obtain more information.

“In the House of Commons last week, [former Scottish first minister] Alex Salmond voted with the Liberal Democrats against Tory moves that would see our internet histories recorded and made available to the intelligence services,” Carmichael said. “Now it seems that a centre established when he was First Minister was at the heart of the mass surveillance of our personal information.”

If it turns out that the Scottish government claims it was not in fact aware of the MILKWHITE program, Carmichael said, it would raise “big questions over the role of the U.K. intelligence services.” And if it were aware and yet “did nothing to raise the alarm, then we need to be told why they were happy for Scots to be left in the dark,” he added.

Scottish police and GCHQ have declined to answer questions about MILKWHITE, citing policy not to comment on “intelligence matters.” The Home Office has also refused to comment, claiming that it never discusses anything derived from leaked documents.