The Met said the information requested may have been “supplied by, or concerning, certain security bodies” that don’t have to abide by normal transparency requirements, such as the secretive surveillance agency Government Communications Headquarters, or GCHQ. The Met also claimed that it “would not be in the public interest” to reveal basic information about the status of the criminal probe because doing so “could be detrimental to any investigations that may be being conducted now or in the future.”
The Met carried out the searches for relevant requested information at its Counter Terrorism Command, according to the refusal notice, which is the unit handling the Snowden investigation. The Counter Terrorism Command operates within the Met’s Specialist Operations department and had a leading role in the Snowden-related detention and interrogation at a London airport in August 2013 of David Miranda, the partner of Intercept co-founder and former Guardian journalist Glenn Greenwald.
via UK Police Deem Snowden Leak Investigation a State Secret – The Intercept.