David Cameron has indicated the government may try and use "tougher measures" against The Guardian to prevent it from publishing further revelations about the activities of British intelligence agencies.
Speaking in the House of Commons on Monday afternoon, the prime minister said while the government had not yet been "heavy handed" in how it responded to the dissemination of leaks from NSA whistle-blower Edward Snowden - it could crack down if it continued.
"We live in a free country so newspapers are free to publish what they want," he said. However he added the articles in The Guardian had made "this country less safe".
And he urged newspapers to use "judgement and common sense" when deciding to publish material. "I don't want to have to use injunctions or D-Notices or the other tougher measures. I think its much better to appeal to newspapers' sense of social responsibility," he said.
But he added: "If they don't demonstrate some social responsibility it would be very difficult for government to stand back and not to act."
D-Notices are issued to editors by government to request they do not publish material in the interests of national security.
Cameron, who was facing questions from MPs on last week's summit of European leaders, also took the opportunity to insist the work of British spies had helped to save lives across the continent. "Our intelligence has also allowed us to warn our EU allies of plots against their people," he said.
The meeting of EU presidents and prime ministers in Brussels was dominated by the allegations that the United States had bugged the phone of German chancellor Angela Merkel. Cameron said he would not comment on the work of British intelligence agencies or whether he believed his phone had been hacked by the Americans - however he pointed to a White House statement that denied the the US had targeted his phone.
Cameron added: "The UK has a very strong, long standing trust based relationship with the United States, not least as part of the 'Five Eyes' partnership."
The revelations about the global activities of American and British intelligence agencies have been hugely embarrassing for Washington and London and have cause a deep diplomatic rift between president Obama and several European allies.