Home Secretary Theresa May confirmed she was briefed in advance of the detention at Heathrow Airport of David Miranda, the partner of a Guardian journalist who has written a series of stories on the US National Security Agency's mass surveillance.
Mrs May added that despite being informed of his detention, she does not make the decisions on who the police do and do not stop.
But she endorsed Mr Miranda's detention, saying: "If it is believed that somebody has in their possession highly sensitive stolen information which could help terrorists, which could lead to a loss of lives, then it is right that the police act and that is what the law enables them to do."
The independent reviewer of terrorism legislation said he will examine the detention of David Miranda at Heathrow Airport.
Nick Clegg has backed David Cameron's decision to send a top civil servant to The Guardian to urge them to destroy classified data.
The Guardian journalist whose partner was held at Heathrow Airport hits out at the UK as he gives ITV News his first British TV interview.