The editor of the Guardian newspaper, a major outlet for revelations based on leaks from former US intelligence contractor Edward Snowden, says the British government threatened legal action against it unless it either destroyed the classified documents or handed them to British authorities.

In an article posted on the British newspaper's website on Monday, Guardian editor Alan Rusbridger said that a month ago, after the newspaper had published several stories based on Snowden's material, a British official advised him: "You've had your fun. Now we want the stuff back."

You've had your fun. Now we want the stuff back. What Guardian editor, Alan Rusbridger wrote that a British official told him.

After further talks with the government, Rusbridger said, two "security experts" from Government Communications Headquarters, the British equivalent of the ultra-secretive US National Security Agency, visited the Guardian's London offices.

In the building's basement, Rusbridger wrote, government officials watched as computers which contained material provided by Snowden were physically pulverised.

"We can call off the black helicopters," Rusbridger says one of the officials joked.

The newspaper's decision to publicise the government threat - and an assertion that it can continue reporting on the Snowden revelations from outside of Britain - appears to be the latest step in an escalating battle between the news media and governments over reporting of secret surveillance programs.

On Sunday, British authorities detained for nine hours the domestic partner of Glenn Greenwald, a Guardian writer who met face to face in Hong Kong with Snowden and has written or co-authored many of the newspaper's stories based on his material.

It was not clear exactly when the incident occurred but Rusbridger gave a vague timeline, suggesting that it happened within the past month or so.