British Prime Minister David Cameron instructed Cabinet Secretary Sir Jeremy Heywood to contact the Guardian to spell out the serious consequences that could follow if it failed to hand over classified material received from Edward Snowden.
Senior Whitehall sources confirmed to the Independent the Prime Minister's central role in trying to limit revelations about UK and US intelligence operations contained in information the whistleblower received from the National Security Agency.
The Daily Telegraph reported that Cameron sanctioned the destruction of computer equipment belonging to the Guardian on national security grounds and was briefed on the police operation to detain the partner of a journalist.
News of Cameron's intervention came as official Home Office and Scotland Yard accounts of the nine-hour detention at Heathrow of the Brazilian partner of a Guardian journalist were contradicted by lawyers involved in the ordeal.
According to the Metropolitan Police, David Miranda - whose partner Glenn Greenwald has led the reporting of stories linked to NSA material supplied by Snowden - was offered legal representation during his questioning and a solicitor was in attendance. The Home Office also claimed the detention was "legally and procedurally sound" and backed in full the Met's account.