In an e-mail Monday to The Associated Press, Mr. Greenwald said that he needed material from Ms. Poitras for articles he was working on related to the N.S.A., and that he had things she needed. “David, since he was in Berlin, helped with that exchange,” Mr. Greenwald wrote.

Keith Vaz, an opposition Labor Party legislator who is chairman of Parliament’s Home Affairs select committee, said he had written to the head of London’s Metropolitan Police Service, which has jurisdiction in the matter, to ask for clarification of what he called an extraordinary case.

“What needs to happen pretty rapidly is, we need to establish the full facts,” he told the BBC. “Now you have a complaint from Mr. Greenwald and the Brazilian government — they indeed have said they are concerned at the use of terrorism legislation for something that does not appear to relate to terrorism. So it needs to be clarified, and clarified quickly.”

The editor of The Guardian, Alan Rusbridger, disclosed on Monday that the British government had sent officials from Government Communications Headquarters, which is known as GCHQ and is the British version of the National Security Agency, to the newspaper’s offices in London to destroy computers containing documents leaked by Mr. Snowden. Mr. Rusbridger said that he had protested that the same information was available elsewhere, but that the officials had insisted on proceeding.

“And so one of the more bizarre moments in The Guardian’s long history occurred — with two GCHQ security experts overseeing the destruction of hard drives in The Guardian’s basement just to make sure there was nothing in the mangled bits of metal which could possibly be of any interest to passing Chinese agents,” he wrote, adding, “We will continue to do patient, painstaking reporting on the Snowden documents, we just won’t do it in London.”