Lawyers for the boyfriend of a journalist who helped publish Edward Snowden's leaked files will on Thursday ask the High Court to prevent the copying of data seized during his Heathrow Airport detention.

David Miranda, 28, the partner of Guardian journalist Glenn Greenwald, was on Sunday detained for nine hours under anti-terror laws and had his laptop, phone and other electronic equipment confiscated.

The High Court in London will on Thursday hear his legal team's application for an injunction preventing the authorities using, copying and sharing data from the seized devices.

In their submission, Miranda's legal team claims he was "subjected to intensive, wide-ranging and intrusive questioning ... but he was not asked, nor was it suggested, that he was involved with terrorist groups, organisations or terrorist activity", The Guardian reported.

Prime Minister David Cameron on Wednesday faced calls to address parliament on why the country's top civil servant pressured the Guardian to destroy or return Snowden's leaked files.

The call from a senior lawmaker came as Deputy Prime Minister Nick Clegg's spokesman said that asking the daily to comply was better than taking legal action over the documents leaked by Snowden, a former US National Security Agency (NSA) contractor.

The Guardian's editor Alan Rusbridger has claimed he was ordered to destroy some of the newspaper's classified Snowden files during a shadowy visit from a senior government official a month ago.

The government confirmed on Wednesday that the official sent to the Guardian was Cabinet Secretary Jeremy Heywood, a politically neutral civil servant who is Cameron's most senior policy advisor.

Keith Vaz, chairman of the parliament's Home Affairs Select Committee, called on Cameron to make a "full statement" to the House of Commons when it returns in September.

"The actions of the cabinet secretary are unprecedented and show that this issue has reached the highest levels of government," he said.

"The prime minister must make a full statement to parliament on the day it returns."

Rusbridger said two security experts from electronic eavesdropping agency GCHQ (Government Communications Headquarters) oversaw the destruction of hard drives on July 20.

Beforehand, the editor had informed government officials that copies of the files, which were encrypted, existed outside Britain and that the newspaper was neither their sole recipient nor their steward.

A senior editor and a Guardian computer expert used power tools to pulverise the hard drives and memory chips.

Based on the documents from Snowden, who has been granted temporary asylum in Russia as he flees a US bid to prosecute him, The Guardian has published details about mass surveillance programmes conducted by the NSA and GCHQ.

Clegg's spokesman said the deputy PM understood concerns about press freedom.

But he "thought it was reasonable for the cabinet secretary to request that The Guardian destroyed data that would represent a serious threat to national security if it was to fall into the wrong hands," the spokesman said.

"The deputy prime minister felt this was a preferable approach to taking legal action."

A Downing Street spokesman told AFP: "We won't go into specific cases, but if highly sensitive information was being held unsecurely, the government would have a responsibility to secure it."

The hard drive destruction and Miranda's detention for nine hours have triggered unease in several other countries.

Russia condemned the "perverse practice of double standards applied by London in the field of human rights".

"The steps undertaken by the British authorities towards The Guardian newspaper are out of synch with the British side's stated commitment to universal human rights standards," the foreign ministry said.

The Council of Europe, a pan-European rights body that is separate from the EU, meanwhile wrote to the British government questioning whether the measures were compatible with its treaty obligations.

"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," wrote the council's Secretary General Thorbjoern Jagland.

Germany's top human rights official was also sharply critical.

Markus Loening, the rights chief at the foreign ministry, expressed "great concern" about media freedom in Britain, and branded Miranda's detention "unacceptable."