They wrote: "It is plainly unsatisfactory to assert that the debate is solely about 'maintaining' capabilities for acquiring communications data.
"The ICT environment has changed so much since 2000 that we ought to be asking ourselves about the appropriate balance between powers given to law enforcement and the agencies and the privacy of the individual."
They argued IMP should also not be debated without considering the power of other new surveillance technologies adopted by the government, such as Automated Number Plate Recognition.
GCHQ, the Cheltenham-based electronic eavesdropping agency that emerged from war time code breaking efforts at Bletchley Park, has pressed hard in Whitehall for massive spending to gather communications. Its classified "Mastering the Internet" project, a key part of the IMP revealed by The Register last month, includes hundreds of millions of pounds of DPI and automated analysis facilities.
While the Home Office's consultation is concerned with future storage arrangements, Mastering the Internet is already underway and focused on obtaining and analysing terabytes of communications data daily.
According to sources, the agency wants to be able to configure DPI equipment inside ISPs remotely, allowing it to harvest data from any new internet applications that might emerge. This would mark another major change from the current arrangements, according to the LSE's report, as the collection of communications data is under the control of the provider, not a government agency.
IMP would be unmatched in the world as a communications surveillance mechanism
Under the Home Office's proposals, once collected, communications data would be stored for two years in a system of federated databases run by providers at a cost to taxpayers of £2bn over 10 years. Ministers also plan to deputise ISPs, mobile operators and phone companies to carry out preliminary analysis by linking different data together into a single record for each customer.
As we reported last week, those proposals have met with a frosty reception from the internet industry, who criticised them as showing a lack of appreciation for their technical capabilities, and naivety over the potential costs.
The LSE's researchers agreed, criticising the Home Office for failing to publish detailed estimates. "We have a substantial number of questions about what is and what is not included in their cost estimates, and from where the costs will be met," they wrote.
In response to the report's findings, the Home office said: "We know that this is a complex and extremely sensitive subject, with a fine balance to be made between protecting public safety and civil liberties.
"Because of this we have launched a public consultation to seek views from interested parties – including communication service providers. We will ensure there are stringent safeguards inbuilt into any future proposals."
Sommer said he was pleased the work - carried out with UK and international experts under the Chatham House rule - will be used as briefing material by Parliamentarians. Their probe, beginning in July, will be the first by a new group, the All Party Parliamentary Group on Privacy, formed to act offer "early warning protection" on privacy issues. Its membership is drawn from MPs and peers on all sides of both Houses and includes David Davis and Lord Carlile, the independent scrutineer of terrorism legislation.
The Home Office said it would cooperate with the Group on Privacy's work.
The full LSE report is available here. ®