Tougher laws are needed to prevent members of the public from revealing official secrets, according to former Scotland Yard commissioner Lord Blair.
The peer insisted there was material the state had to keep secret, and powers had to be in place to protect it.
The intervention comes after police seized what they said were thousands of classified documents from David Miranda – the partner of Guardian journalist Glenn Greenwald, who has been reporting leaks from former US intelligence officer Edward Snowden.
The Home Office has defended the use of anti-terror laws to detain and question Mr Miranda at Heathrow airport earlier this month.
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Lord Blair told BBC Radio 4's Broadcasting House programme: "The state has to have secrets – that's how it operates against terrorists.
"It has to have the right to preserve those secrets and we have to have a law that covers a situation when somebody, for all sorts of wonderfully principled reasons, wishes to disclose those secrets.
"It just is something that is extremely dangerous for individual citizens to (make) those secrets available to the terrorists."
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Lord Blair said the threat from international terrorism was "constantly changing" and there was a need to "review the law".
He warned there was a "new threat which is not of somebody personally intending to aid terrorism, but of conduct which is likely to or capable of facilitating terrorism" – citing the examples of information leaks related to Bradley Manning and the WikiLeaks website.
He went on: "Most of the legislation about state secrets is in the Official Secrets Act and it only concerns an official.
"I think there is going to have to be a look at what happens when somebody possesses material which is secret without having authority."
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