The Interception Modernisation Programme is a plan for a database (condemned by critics as a "Big Brother" database) of every phone call, email, text and web browsing session. Conservatives have been unable to extract from ministers an estimate of how much it will cost, although a figure of £12 billion has been cited in the media.
Shadow Minister for the Cabinet Office and Shadow Chancellor of the Duchy of Lancaster Francis Maude has recently received a written answer on the matter:
"To ask the Secretary of State for the Home Department what the estimated (a) set-up and (b) running costs of the interception modernisation programme are. 
Mr. Coaker: The Interception Modernisation Programme (IMP) will require a substantial level of investment which will need to tie in with the Government’s three year CSR periods. The scale of overall economic investment is very difficult to calculate because of the complexity of the programme and wide ranging implementation solutions currently being considered.
Given the commercial and national security sensitivities, the precise costs of the programme cannot be disclosed. Further detail on budgetary estimates for the IMP will however become available once the public consultation process (announced by the Home Secretary on 15 October 2008) commences."
This is a subject on which ConservativeHome will want to keep its own eye.