Prime Minister David Cameron on Wednesday faced calls to address parliament on why Britain'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 left-leaning daily to comply was better than taking legal action over the secret documents handed over by the former US National Security Agency (NSA) contractor.
Meanwhile Britain came in for sharp criticism over the detention of Brazilian national David Miranda, the boyfriend of Guardian journalist Glenn Greenwald who worked with Snowden on the leaks.
Miranda, who assisted Greenwald with the material, was held and questioned for nine hours on Sunday under anti-terror laws as he travelled from Berlin to the couple's home in Rio de Janeiro.
In recent months, the Guardian has published a series of revelations from the thousands of documents given to it by Snowden, who has been granted temporary asylum in Russia as he flees a US bid to prosecute him.
The Guardian published details about mass surveillance programmes conducted by the NSA and its British counterpart, the Government Communications Headquarters (GCHQ).
Two months ago, Cabinet Secretary Jeremy Heywood, Britain's top civil servant, issued the newspaper with the ultimatum to return or destroy the material, or face court action, it emerged Tuesday.
Politically neutral, Heywood is Cameron's most senior policy advisor and sits beside him at the cabinet table in Downing Street.
"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," a Downing Street spokesman told AFP.
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 on October 8.
"The actions of the cabinet secretary are unprecedented and show that this issue has reached the highest levels of government," he said.
"It explains why Downing Street, the White House and the home secretary were briefed in advance about David Miranda's detention.
"It's clear that they have taken a proactive stance, not just in terms of the destruction of the information held by the Guardian but also the involvement of those journalists who have written about Edward Snowden.
"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."
The Guardian's editor Alan Rusbridger said two GCHQ security experts oversaw the destruction of hard drives on July 20.
Beforehand, he had informed government officials that copies of the files existed outside Britain and that the newspaper was neither the sole recipient or steward of the files.
A senior editor and a Guardian computer expert used angle grinders and drills to pulverise the hard drives and memory chips on which the encrypted files had been stored.
A spokesman for Clegg said the deputy PM understood concerns about press freedom and civil liberties.
However, 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."
There was an understanding that destroying the material "would not impinge on the Guardian's ability to publish articles about the issue, but would help as a precautionary measure to protect lives and security."
Meanwhile the detention of Miranda, 28, has caused an international outcry and sparked protests from Brazil.
The Brazilian's lawyers are challenging the legality of his detention.
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 including freedom of the press," the foreign ministry said.
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".
Loening said he was "deeply shocked" and "the red line was crossed".
German Chancellor Angela Merkel's spokesman said press freedom and the protection of journalistic sources were "crucial principles".