MI6 chief Sir John Sawers said the leaks from NSA whistleblower Edward Snowden "have been damaging and put operations at risk."
Al-Qaeda is "lapping up" the leaks and Britain's enemies are rubbing their hands with glee, the British intelligence chief added.
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Nigel Farage warned on Friday Britain was "far less safe" and exposed to Cologne-style sex attacks because of open-door immigration.
Arthur Simpson-Kent, 48, admitted killing Ms Blake and their sons according to his lawyer.
Two brothers have been arrested on suspicion of murder after their parents were found dead in their own home over the weekend.