British Prime Minister David Cameron on Wednesday faced calls to address parliament on why the country's top civil servant pressured the Guardian newspaper to destroy or return Edward 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 the former US National Security Agency (NSA) contractor.
Britain meanwhile faced fresh international criticism over both the computer incident and the detention at the weekend of David Miranda, the boyfriend of Guardian journalist Glenn Greenwald who worked with Snowden on the leaks.
Miranda's lawyers said their application for an injunction preventing authorities from copying and sharing data from electronic devices seized during his detention will be heard at the High Court on Thursday.
The left-liberal 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 British parliament's Home Affairs Select Committee scrutiny body, 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. We need to know the full facts. Nothing less will do."
Home Secretary Theresa May later said police were right to detain Miranda.
"If the police believe someone has in their possession highly sensitive stolen information that could help terrorists that could lead to a loss of life, it is right the police should act," she told BBC Radio 4.
Rusbridger said two security experts from Britain's 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.
-- 'Preferable approach to taking legal action' --
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 under anti-terror laws as he travelled through London Heathrow Airport on Sunday 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 May questioning whether the measures were compatible with Britain's 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 also sharply criticised the moves on the Guardian.
Markus Loening, the rights chief at the foreign ministry, expressed "great concern" about media freedom in Britain, and branded Miranda's detention "unacceptable".