guardian newspaper
David Cameron believed to have ordered senior Whitehall officials to warn the Guardian about Snowden files  (Reuters)

Prime Minister David Cameron is believed to have ordered a crackdown on the Guardian after it published top-secret intelligence documents leaked by whistleblower Edward Snowden.

The Independent, citing Whitehall sources, claimed that Cameron told Cabinet Secretary Sir Jeremy Heywood to contact its rival newspaper and warn management of severe punishment if it refused to hand over classified material provided by Snowden.

This disclosure appears to confirm earlier claims from Guardian editor Alan Rusbridger that he was contacted by senior government officials and pressured into providing the material.

Meanwhile the Telegraph, quoting a contact at Downing Street, caimed Cameron "explicitly" sanctioned the destruction of computer equipment containing information from Snowden at the Guardian's offices in London.

The source at No 10 also claims Cameron was "kept abreast" of the operation to detain David Miranda, whose partner Glenn Greenwald broke the Snowden story for the Guardian.

The detention of Miranda for nine hours at Heathrow Airport has sparked widespread condemnation, while Miranda has threatened legal action and Greenwald has vowed to publish more information from Snowden in defiance of the Government's attempted crackdown.

Nonetheless the coalition has defended the decision to detain Miranda under controversial Schedule 7 of the Terrorism Act, despite the legal action intended by Greenwald's partner.

It is still unclear who led the operation, specifically whether or not it was Scotland Yard. There is also speculation that MI6 officials could have been involved in questioning Miranda.

Home Secretary Theresa May has also confirmed she was informed in advance of Miranda's detention, however she stressed it was the police's decision. The Home Office said the action was "legally and procedurally sound", fully backing the Met police version.

However US authorities, who were given a "heads up" before Miranda was questioned, have distanced themselves from Britain's handling of leaked documents at the Guardian's office in London. Two GCHQ experts were present to make sure the documents containing sensitive information are destroyed.

When asked about the incident, White House spokesperson Josh Earnest said: "It's very difficult to imagine a scenario in which that would be appropriate here."