Details of secret warrants used for mass surveillance in the UK and abroad have been revealed for the first time in an official new report.

The Interception of Communications Commissioner’s Office (IOCCO) has published an unprecedented review of mass surveillance carried out via Section 94 of the Telecommunications Act 1984.

The continued use of this relatively old piece of legislation to carry out large-scale spying was first avowed last year, when home secretary Theresa May told MPs that "successive governments have approved the security and intelligence agencies' access to such communications data from communication service providers" using Section 94 of the Act.

Unlimited power to require telecoms companies to do, or not do, anything, without any limit of time was granted to home secretaries under the law. The warrants are so secret that recipients are not allowed to mention their existence in any way, and they may even be forbidden from keeping copies.

The IOCCO's report reveals that 15 Section 94 "directions" for mass surveillance were given between 2001 and 2012, and that all of these remain in force. All of them are for traffic data—that is, metadata—and all require "regular feeds of bulk communications data to be disclosed." Data is held for a year, and then automatically destroyed on a daily basis. Requests for the warrants came from GCHQ and MI5, but not MI6, and were made on the grounds of "national security."

Exactly how many requests were made for data from those mass surveillance directions last year were also disclosed in the report: "In 2015 GCHQ identified 141,251 communications addresses or identifiers of interest from communications data acquired in bulk pursuant to section 94 directions which directly contributed to an intelligence report."

Similarly: "In 2015 the Security Service [MI5] made 20,042 applications to access communications data obtained pursuant to section 94 directions. These applications related to 122,579 items of communications data."

Interception of Communications' commissioner Sir Stanley Burnton noted in his summary that compiling the report was difficult. First, because of the extreme secrecy surrounding this whole area: "the section 94 directions are secret as allowed for by statute. During our drafting of this report we have had to be mindful of the fact that none of the section 94 directions under our oversight have been laid in Parliament by the Secretary of State and therefore they remain subject to the statutory secrecy provisions."

Secondly, "section 94 of the Telecommunications Act 1984 does not include any provision for independent oversight or any requirements for the keeping of records." Finally, there are no "codes of practice for the exercise or performance and duties relating to section 94 directions."

The commissioner, who made extensive recommendations in the report, added that "relevant intelligence and law enforcement agencies should introduce [those recommendations] to clarify and bring consistency to the procedures in place, remedy the lack of record-keeping requirements and ensure that we are able to undertake our oversight of the giving and use of section 94 directions properly." He said they must be implemented "without delay."

The almost complete opacity of the system, combined with the unlimited power of directions made under Section 94 has led to civil liberties' campaign group Big Brother Watch to label them "clearly one of, if not the most insidious tool available to the intelligence agencies."

It's worth noting that Section 94 will be repealed as part of the overhaul of surveillance currently being carried out by parliament. As Sir Stanley writes: "The provisions in the Investigatory Powers Bill and the associated draft Codes of Practice are an opportunity to remedy these issues."

However, Big Brother Watch points outs out that the IOCCO's report confirmed its earlier fears about surveillance oversight:

Throughout the scrutiny of the IP Bill we have stressed that Ministers are not required to come and tell Parliament or the House of Lords about warrants relating to surveillance. We gave evidence to the Joint Committee on the Investigatory Powers Bill which made that clear. Throughout we have been told that we are wrong and that Ministers are answerable to Parliament and that if they do things the country doesn’t like then we can vote them out. This report shows in black and white that that is simply not the case. Rather than use a warrant which required sign of by another official and annual renewal, the Home Office chose to use Section 94, to avoid any external oversight or sign off, to avoid the inconvenience of renewal of the direction and to avoid the need to publicly or even privately declare the direction existed.

Big Brother Watch says that the obvious lesson to be learned from the latest information on the secret use of Section 94 is that the proposed "double lock" authorisation in the IP Bill, involving both a minister and a judicial commissioner, must be strengthened.

It said: "The review and approve lock currently in the Bill may be an improvement to the solo sign off this report has highlighted, but it is far off the mark when it comes to ensuring that surveillance against all UK citizens is subject to the strongest independent authorisation methods available."