The decision to send top civil servant Sir Jeremy Heywood to urge the Guardian to destroy classified data was backed by Nick Clegg it has been revealed.
A spokesman for the Deputy Prime Minister said he was “keen to protect” the newspaper’s freedom to publish while safeguarding national security.
Mr Clegg agreed to the move on the understanding that destruction of the material would not impinge on the Guardian’s ability to publish articles, he added.
It emerged last night that Cabinet Secretary Sir Jeremy was directed by David Cameron, backed by Mr Clegg, to contact the Guardian about classified material handed over by Edward Snowden.
The intervention ordered by No 10 came to light following the detention at Heathrow Airport under terror laws of David Miranda, partner of Guardian journalist Glenn Greenwald who has worked with Snowden on a series of security services exposes.
A spokesman for Mr Clegg said: “We understand the concerns about recent events, particularly around issues of freedom of the press and civil liberties. The independent reviewer of terrorism legislation is already looking into the circumstances around the detention of David Miranda and we will wait to see his findings.
“On the specific issue of records held by the Guardian, the Deputy Prime Minister 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 Deputy Prime Minister felt this was a preferable approach to taking legal action. He was keen to protect the Guardian’s freedom to publish, whilst taking the necessary steps to safeguard security.
“It was agreed to on the understanding that the purpose of the destruction of 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.”
Scotland Yard and the Home Office have insisted the actions of officers who detained David Miranda at Heathrow were proper.
Theresa May confirmed yesterday that she had been briefed in advance about the possible detention of Mr Miranda and a spokesman said No 10 was “kept abreast of the operation in the usual way”. It is understood Mr Clegg was not notified in advance.
Mrs May told the BBC: “If it is believed that somebody has in their possession highly-sensitive stolen information which could help terrorists, which could lead to a loss of lives, then it is right that the police act and that is what the law enables them to do.”
But the Home Secretary, who has come under pressure to explain how much the Government knew about the planned detention of Mr Miranda after the White House said it had been given a “heads up”, said there were safeguards in place to make sure such arrests were conducted properly.
“I was briefed in advance that there was a possibility of a port stop of the sort that took place,” she said.
“But we live in a country where those decisions as to whether to stop somebody or arrest somebody are not for me as Home Secretary, they are for the police to take. That’s absolutely right that they have their operational independence and long may that continue.”
Mr Miranda was detained at Heathrow Airport under Schedule 7 of the Terrorism Act 2000 as he changed planes on a journey from Berlin to his home in Brazil.
He claimed he was held for nine hours by agents, who questioned him about his “entire life” and took his “computer, video game, mobile phone, my memory card – everything”.
Schedule 7 applies only at airports, ports and border areas, allowing officers to stop, search, question and detain individuals.
Its use has been criticised by Mr Greenwald – the reporter who interviewed Snowden – as a “profound attack on press freedoms and the news-gathering process”, and has sparked concern on the use of terror laws.
Lawyers for Mr Miranda have written to both Mrs May and Britain’s most senior police officer challenging the legality of the decision to detain him for nine hours using Schedule 7.
They have also demanded assurances that none of the material will be disclosed or shared or used and, if guarantees are not given, will apply for an injunction, the company said.
Foreign Secretary William Hague said: “The Government clearly has a duty if information is held insecurely and could be damaging to our national security to try to make sure that it is recovered or destroyed.
“It’s a very simple matter.”