MPs and Lords will launch an investigation into the Home Office's £2bn plan to store details of every online communication, after a critical report by the London School of Economics branded it unrealistic, disproportionate and misleading.
Representatives from all sides of both Houses will use the report as the starting point of a probe into the Interception Modernisation Programme (IMP) in July.
The LSE's academics today questioned whether the government had fully appreciated the legal and democratic implications of IMP. They said thousands of planned Deep Packet Inspection (DPI) probes to harvest data on web browsing, email, VoIP calls and instant messenger conversations from inside ISP networks would blur the legislative and ethical lines between communications data and communications interception.
In its consultation document on IMP, published after delays in April, the Home Office emphasised that the system would only collect information on who contacts whom, when, where and how. It would not, then-Home Secretary Jacqui Smith said, monitor the content of communications.
Current legislation governing surveillance - the Regulation of Investigatory Powers Act (RIPA) - draws a strong distinction between communications data and communications interception. The former requires only the approval of a senior law enforcement or intelligence officer, the latter a warrant signed by the Home Secretary. Officials aim to maintain the separation if IMP is implemented.
But according to Professor Peter Sommer, a leading expert witness on communications data and leader of the LSE research, DPI systems make that impossible. "RIPA is based on the old fashioned telephone," he said.
"With internet technology you have to collect everything and then throw away what the law does not allow you to have or use.
"We think that at a practical level, the communications data/interception distinction will be impossible to interpret both for ISPs and the courts. Moreover the existing balance of protections against abuse will also be lost."
His comments echo the concerns of Register sources over the past 12 months. Several have cited the example of a Facebook conversation: for authorities to discover who is at the other end the DPI equipment will have to look inside the content payload.
Such grey areas could spell trouble for prosecution cases, according to the LSE's report. The content of communications is currently inadmissable in court, so a defence might be able to make technical arguments against allowing evidence obtained via IMP.
Home Office, law enforcement and intelligence figures have argued throughout the debate on IMP that it will merely "maintain capability" for authorities to access communications data as internet technologies come to dominate electronic communication. That line was dismissed by the LSE researchers because advances in automated analysis would enable much more data to be interrogated than at present.