"We do not spend our time listening to the telephone calls or reading the emails of the majority," GCHQ boss Sir Iain Lobban told the committee.
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United Airlines has apologised for its initial response after a passenger was injured as he was forcibly removed from an overbooked flight.
It is said that the teenager attacked and raped the woman, in her forties, on April 19 near to a park in Kidbrooke, south-east London.