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.
...
Mr. Miranda told reporters in Rio that he had been subjected to deep questioning at Heathrow. “I stayed in a room, there were six different agents, entering and leaving, who spoke with me,” he said. “They asked questions about my whole life, about everything. They took my computer, video game, cellphone, memory thumb drives — everything.”
Mr. Greenwald said that all of the documents encrypted on the thumb drives came from the trove of materials provided by Mr. Snowden.
Source: http://www.nytimes.com/2013/08/20/world/europe/britain-detai...
And:
He had spent the previous week in Berlin visiting Laura Poitras, a documentary filmmaker who has also been helping to disseminate Mr. Snowden's leaks, to assist Mr. Greenwald. The Guardian had paid for the trip, Mr. Greenwald said, and Mr. Miranda was on his way home to Rio de Janeiro.
Mr. Miranda was in Berlin to deliver documents related to Mr. Greenwald's investigation into government surveillance to Ms. Poitras, Mr. Greenwald said. Ms. Poitras, in turn, gave Mr. Miranda different documents to pass to Mr. Greenwald. Those documents, which were stored on encrypted thumb drives, were confiscated by airport security, Mr. Greenwald said. All of the documents came from the trove of materials provided to the two journalists by Mr. Snowden. The British authorities seized all of his electronic media — including video games, DVDs and data storage devices — and did not return them, Mr. Greenwald said.
Source: http://theweek.com/article/index/248385/the-miranda-mess
Having read that, I now believe the British were justified in detaining Miranda, though doing so for 9 hours was clearly excessive. What on earth was Greenwald thinking though letting his spouse, who lacks any kind of journalistic privilege, travel through the UK while carrying classified leaked NSA and GCHQ documents? It was foolish at best.