The Guardian knows that it compromised Britain's national security when it decided to use information leaked by a former National Security Agency employee, the Prime Minister said today.
David Cameron said it was plain to see that the Edward Snowden affair had been damaging to the UK and that in agreeing to dispose of the relevant information it had obtained, the newspaper effectively accepted its involvement in this.
He said: "I think the plain fact is that what has happened has damaged national security, and in many ways the Guardian themselves admitted that when they agreed, when asked politely by my national security adviser and Cabinet Secretary (Sir Jeremy Heywood) to destroy the files they had, they went ahead and destroyed those files.
"So they know that what they are dealing with is dangerous for national security."
Mr Cameron's comments came in an answer during Prime Minister's Questions in the Commons.
Former defence secretary Dr Liam Fox had called for an investigation into the Guardian's role to determine whether or not it had indeed threatened Britain's national security.
He asked: "Can we have a full and transparent assessment about whether the Guardian's involvement in the Snowden affair has damaged Britain's national security?"
He added: "And will you agree that it is bizarre that, from some, the hacking of a celebrity phone demands a prosecution, but leaving the British people and the security personnel more vulnerable is opening a debate?"
Cameron replied: "I think it's up to select committees in this House if they want to examine this issue and make further recommendations."
Government figures are split over whether or not the Guardian was right to publish secret material leaked by Edward Snowden, which revealed the extent of mass surveillance programmes operated by the US National Security Agency and Cheltenham-based GCHQ.
Yesterday, Deputy Prime Minister Nick Clegg said technical details about the operations of spies should not be published in newspapers.
But his Liberal Democrat colleague Business Secretary Vince Cable expressed concerns about the level of scrutiny the newspaper was now facing, saying it had performed "a very considerable public service".
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