The state-supervised destruction of a newspaper's hard drives and the detention of a journalist's partner under terror laws could have a "chilling effect" on press freedom, the head of Europe's top human rights organisation has warned home secretary Theresa May.

The state-supervised destruction of a newspaper's hard drives and the detention of a journalist's partner under terror laws could have a "chilling effect" on press freedom, the head of Europe's top human rights organisation has warned home secretary Theresa May.

In an intervention more often directed at countries such as Turkey and Russia, the secretary general of the Council of Europe, Thorbjørn Jagland, has written to May asking her to explain how the actions were compatible with Britain's obligations under the European Convention on Human Rights.

"These measures, if confirmed, may have a potentially chilling effect on journalists' freedom of expression as guaranteed by Article 10 of the European Convention on Human Rights," he wrote.

"I would therefore be grateful to you if you could provide information on these reports and comment on the compatibility of the measures taken with the United Kingdom's obligations under the Convention."

The Guardian destroyed a hard drive containing a copy of the secret documents leaked by US whistleblower Edward Snowden under the supervision of GCHQ officers

It agreed to the move following sustained pressure from Government, with Cabinet Secretary Sir Jeremy Heywood directed by the Prime Minister to contact the newspaper about the classified material.

May has said it was the "right and proper" action in the circumstances.

"If Government believes information that could be of help to terrorists is potentially being held insecurely, could fall into the wrong hands, I think it is right the Government should act," she said.

And Foreign Secretary William Hague said there was a clear "duty" to intervene.

The plan was approved by Deputy Prime Minister Nick Clegg whose spokesman said he considered it a "preferable approach to taking legal action".

But Labour's Keith Vaz said the actions were "unprecedented" and called on the Prime Minister to make a "full statement" to Parliament on the day it returns after the summer break.

Meanwhile, lawyers acting for David Miranda will take his case to the High Court today.

The partner of Guardian journalist Glenn Greenwald was held for nine hours at Heathrow under anti-terror laws last weekend.

His lawyers have applied for an injunction preventing the police or government using, copying and sharing data from electronic devices seized from him during his detention.

Two judges will also hear their argument that Miranda's detention at Heathrow Airport was a misuse of Schedule 7 of the Terrorism Act 2000 and breached his human rights.

Scotland Yard says the detention was "legally and procedurally sound" but that is disputed by Miranda's lawyers and has been questioned by a former Lord Chancellor.

Lord Falconer, who helped introduce the law under the last Labour government, insisted the powers were designed to be used against those suspected to be terrorists.