Glenn Greenwald, the journalist behind a series of explosive stories about the activities of the US and British intelligence agencies, has accused a Tory MP of lying.
On Wednesday, Greenwald appeared before the European Parliament to give evidence about the revelations based on information obtained from NSA whistle-blower Edward Snowden.
During the session Greenwald was asked by a Conservative MEP Timothy Kirkhope whether The Guardian had given him files that he did not originally hold. The British government has accused The Guardian of damaging national security by publishing stories based on the documents.
Greenwald pointedly refused to answer Kirkhopes question. He said: "Fortunately journalists don't have to answer to government officials about what their sources gave them, or how it is that they got their material."
One of the harshest critics of the newspaper has been Conservative MP Julian Smith - who was watching the exchanges from London. He tweeted: "So @ggreenwald confirms to @TimKirkhopeMEP that @guardian gave him files he didn't originally have."
However Greenwald hit back, accusing Smith of misrepresenting his reply. "I said nothing of the sort. You just fabricated that," he tweeted.
Writing on his blog, Greenwald expanded:
This statement is a lie. It's the exact opposite of reality. Rather than "confirm" any of that, I expressly refused to answer Kirkhope's questions about those matters, explaining that journalistic freedom means that journalists do not have to answer to political officials about the sources of their reporting or their journalistic process.
But Smith refused to back down as the Twitter spat continued.