Downing Street and the Home Office are being challenged to answer in public claims that Russia and China have broken into the secret cache of Edward Snowden files and that British agents have had to be withdrawn from live operations as a consequence.
The reports first appeared in the Sunday Times, which quoted anonymous senior officials in No 10, the Home Office and security services. The BBC also quoted an anonymous senior government source, who said agents had to be moved because Moscow gained access to classified information that reveals how they operate.
Privacy campaigners questioned the timing of the report, coming days after a 373-page report by the independent reviewer of terrorism legislation, David Anderson QC, which was commissioned by David Cameron. Anderson was highly critical of the existing system of oversight of the surveillance agencies and set out a series of recommendations for reform.
A new surveillance bill, scheduled for the autumn, is expected to be the subject of fierce debate.