LONDON -- Alan Rusbridger, the mop-haired, soft-spoken editor of The Guardian newspaper, finds himself in a shadowy battle with the British government over purloined secrets that the government will have a hard time winning in the Internet age.
The Guardian, which leans left and used to see itself as the voice of Britain's socially conscious middle class, has struck a more combative tone in the last few years. It was deeply involved in publishing the WikiLeaks material and with that organization's impresario, Julian Assange, and now Glenn Greenwald and t Edward J. Snowden, the former National Security Agency contractor who leaked classifed information to Glenn Greenwald, ablogger for The Guardian.
Having gone global and remained free to readers on the Web, with a newsroom in New York as well as in London, The Guardian is a much harder news organization than most to intimidate or censor, as the British government, with no written constitution or bill of rights to enshrine protections of free speech, has discovered.
But the tale of the last two months, as Mr. Rusbridger tells it, at least, is an extraordinary one of attempted political interference. Agents of the British government descended on The Guardian's offices to monitor three executives as they physically destroyed computer hard drives containing some of the classified material that Mr. Snowden downloaded from American intelligence databases and gave to Mr. Greenwald and others.
"You have powerful protections in America that we don't," Mr. Rusbridger, 59, said Tuesday in an interview after publishing an op-ed article in his paper describing some of the government's actions.
In conversations with him, the British government threatened the paper with "prior restraint," he said, to stop it from publishing material, and then demanded that The Guardian return or destroy the classified material it was holding.
"It was quite explicit: we had to destroy it or give it back to them," Mr. Rusbridger said in an earlier interview with the BBC. "I explained that there were other copies, not within the U.K., so I couldn't see the point of destroying one copy. But because we had other copies I was happy to destroy a copy in London."
The United States has sought the extradition of Mr. Snowden, now in Russia, but it has not acted to restrain newspaper publication or gone into newspaper offices to seize or destroy files and hard drives, as in Britain.
Mr. Rusbridger, Guardian editor since 1995, said he was prompted to describe the government's actions after the British police detained Mr. Greenwald's partner, David Michael Miranda, at Heathrow Airport on Sunday, on his way home from Berlin to Rio de Janeiro. Mr. Miranda had met another of those aiding Mr. Snowden, the filmmaker Laura Poitras, and was carrying encrypted material from her back to Mr. Greenwald in Brazil.
Mr. Miranda, a Brazilian, was held in the transit area of the airport under Schedule 7 of Britain's Terrorism Act 2000 for the legal maximum of nine hours; he was questioned and his electronic equipment seized before being released without charges.
He and Mr. Greenwald intend to file a lawsuit over the detention, Mr. Rusbridger said, "because it's not clear that he was actually committing any offense in carrying material through Heathrow."
The British government has defended the detention. After saying little on Sunday or Monday, a Home Office spokeswoman said the police had been looking for "stolen information" that could be of use to terrorists.
"If the police believe that an individual is in possession of highly sensitive stolen information that would help terrorism, then they should act, and the law provides them a framework to do that," the spokeswoman said. "Those who oppose this sort of action need to think about what they are condoning."
The prime minister's office was kept informed, as was the American government, which denied having asked Britain to take any action against Mr. Miranda.
Mr. Rusbridger sees the detention as an act of intimidation.
Using terrorism legislation that "offers none of the protections that exist in mainland Britain is quite a disturbing new turn," he said.
A lawyer for Mr. Miranda, Gwendolen Morgan, told The Guardian that the police used the antiterrorism laws to bypass normal statutory procedures for seeking confidential journalistic material under the 1984 Police and Criminal Evidence Act.
"This act is likely to have a chilling effect on journalists worldwide, and is emphatically not what Parliament intended Schedule 7 powers to be used for," Ms. Morgan told The Guardian.
Lawyers argued that the detention was also an unlawful "deprivation of liberty" under the European Convention of Human Rights.
Mr. Rusbridger said that two months ago he was contacted by "a very senior government official claiming to present the views of the prime minister," David Cameron. There were two meetings in which officials "demanded the return or the destruction of the material we were working on," and in other meetings, he said, officials said: "You've had your fun, now we want the stuff back," and, "You've had your debate, there's no need to write any more."
The officials then threatened legal action to obtain the documents. Then two security experts from Britain's Government Communications Headquarters, known as G.C.H.Q., the counterpart to the American National Security Agency, came to oversee the destruction of hard drives in The Guardian basement by Guardian executives, Mr. Rusbridger said.
He called it "one of the most bizarre moments in The Guardian's long history."
Efforts to prevent publication of Snowden-related material began on June 7, when defense officials issued a confidential notice to newspapers and broadcasters in an attempt to limit the coverage of Mr. Snowden's revelations about surveillance tactics employed by intelligence agencies in Britain and the United States.
Editors were reminded not to publish information that could "jeopardize both national security and possibly U.K. personnel." The notice followed The Guardian's first publication of details of the American intelligence-gathering program called Prism.
Now, it is not just the opposition Labour Party that is questioning the use of the terrorism laws in this case to seize material intended for journalism, which in countries like the United States would be under more legal protection. David Davis, a Conservative member of Parliament, said that the responses of the Home Office fail "Logic 101."
"'If you're not on our side, you're on the side of the terrorists,' is what they're trying to say," Mr. Davis said.
Robert Wintemute, a professor of human rights law at King's College, London, said that "I hope this is an aberration rather than a signal of a wider clampdown" on press freedom and human rights. "I do think Greenwald and Miranda should bring this to court, because winning in court will rein in the government's powers," he said.
Kimiko de Freytas-Tamura contributed reporting.
This article originally appeared in The New York Times.