ALAN Rusbridger, the Guardian editor, has publicly spoken out about press freedom, whistleblowing and national security as he insisted the decision to detain Brazilian David Miranda under counter-terrorism legislation was a "clear misuse" of the law.

His remarks, at the Edinburgh International Book Festival, came as Scotland Yard and the UK Government's independent reviewer of anti-terror laws said they were each launching investigations into the case.

Mr Miranda, 28, the partner of Guardian journalist Glenn Greenwald, who has worked with US whistleblower Edward Snowden on a series of security services exposes, was detained at Heathrow Airport for nine hours on Sunday under Section 7 of the 2000 Terrorism Act.

This week, it was revealed David Cameron directed Sir Jeremy Heywood, the Cabinet Secretary, to ensure classified material obtained by the Guardian was destroyed.

Mr Rusbridger said of the Brazilian's detention at Heathrow: "It seems to me a clear misuse of a law."

He called for a debate about surveillance, praised the value of the information leaked by Mr Snowden and called "staggering" US soldier Bradley Manning's 35-year jail term for releasing government secrets.

"It cannot be that a small group of 'securocrats' get to make the rules, that no-one's allowed to write about it, if you blow the whistle on it you spend the rest of your life in prison and it's all discussed in a very small clique of people in parliament," he said.

"What Snowden has done is already incredibly valuable. He has already changed how this is going to be done in future and from my point of view, as the editor of a newspaper, I will carry on doing what I can do to aid that debate."

David Anderson, the independent reviewer of terror laws, said he would examine their use to detain Mr Miranda.