Two journalists at the centre of the Edward Snowden mass-surveillance revelations say British claims that spies have been pulled from operations because Russia and China have cracked Snowden's files are full of contradictions and likely false.

Citing anonymous and unverified government sources, Britain's Sunday Times newspaper said in a report this weekend that Britain has pulled out agents from operations in "hostile countries" after Russia and China cracked secrets in the documents leaked by former U.S. National Security Agency contractor Edward Snowden.

Security service MI6, which operates overseas and is tasked with defending British interests, has removed agents from certain countries, the Sunday Times asserted, citing unnamed officials at the office of British Prime Minister David Cameron, the Home Office (interior ministry) and security services.

But journalists Glenn Greenwald and Ryan Gallagher, who have worked with the Snowden files and reported on them, including for CBC News, said the Sunday Times article is full of contradictions and likely falsehoods.

The newspaper provided no evidence aside from the anonymous sources to bear out the claims.

Snowden downloaded tens of thousands of secret files from security agencies in the United States and Britain in 2013, and leaked details about mass surveillance of phone and internet communications. Some of the spy programs disclosed by his leaks have since been ruled illegal in both the U.S. and Britain.

The United States wants Snowden to stand trial after he leaked classified documents, fled the country and was eventually granted asylum in Moscow in 2013.

Snowden said encrypted files were secure

He ended up in Russia after leaving Hong Kong for Latin America, and although he said in 2013 that the encrypted files remained secure, Britain believes both Russia and China have cracked documents which contain details that could allow British and American spies to be identified, the Times report said, citing officials.

British Foreign Secretary Philip Hammond alleged Snowden had done a huge amount of damage to the West's ability to protect its citizens.

"As to the specific allegations this morning, we never comment on operational intelligence matters so I'm not going to talk about what we have or haven't done in order to mitigate the effect of the Snowden revelations, but nobody should be in any doubt that Edward Snowden has caused immense damage," he told Sky News.

But Greenwald, one of the journalists who first broke news of the files and was part of the team that won a Pulitzer Prize for reporting on Snowden's NSA revelations, said the Times article was "filled with falsehoods."

Greenwald wrote on the The Intercept, the news website he co-founded, that the article "gives voice to banal but inflammatory accusations that are made about every whistleblower from Daniel Ellsberg to Chelsea Manning."

"It offers zero evidence or confirmation for any of its claims," he writes. "The 'journalists' who wrote it neither questioned any of the official assertions nor even quoted anyone who denies them. It's pure stenography of the worst kind."

Greenwald pointed to a U.S. Defence Department document, obtained by Vice News under access to information, that showed U.S. government officials have been keen to leak information to the media to try to discredit Snowden.

No evidence of harm

An official at Cameron's office was also quoted in the Times piece saying there was "no evidence of anyone being harmed" — seeming to directly contradict another anonymous official in the same report who said Snowden had "blood on his hands." A spokeswoman at Cameron's office declined to comment when contacted by Reuters.

A Home Office source told the newspaper that Russian President Vladimir Putin did not grant Snowden asylum for nothing.

"His documents were encrypted but they weren't completely secure and we have now seen our agents and assets being targeted," the source said.

Another journalist who worked extensively on the Snowden leaks, Ryan Gallagher, said that claim is unlikely to be true.

"I've reviewed the Snowden documents and I've never seen anything in there naming active MI6 agents," Gallagher wrote on Sunday. He said the Times piece "contains some pretty dubious claims, contradictions and inaccuracies."

Greenwald also noted that Snowden has said "unequivocally" that he didn't take any classified files with him when he left Hong Kong, making it difficult to claim Russia would have gotten its hands on the cache of documents.

Both Greenwald and Gallagher have co-written multiple articles about the Snowden files in collaboration with CBC journalists for CBC's website.

British security agencies declined to comment to Reuters about the claims in the Sunday Times piece.

The Russian and Chinese governments were not immediately available for comment.

Push for expanding surveillance powers

The revelations about the impact of Snowden on intelligence operations comes days after Britain's terrorism law watchdog said the rules governing the security services' abilities to spy on the public needed to be overhauled.

Conservative legislator and former minister Andrew Mitchell said the timing of the report was "no accident."

"There is a big debate going on," he told BBC radio. "We are going to have legislation brought back to Parliament (...) about the way in which individual liberty and privacy is invaded in the interest of collective national security.

"That's a debate we certainly need to have."

Cameron has promised a swath of new security measures, including more powers to monitor Britons' communications and online activity in what critics have dubbed a "snoopers' charter".

Britain's terrorism laws reviewer David Anderson said on Thursday the current system was "undemocratic, unnecessary and — in the long run — intolerable".

He called for new safeguards, including judges not ministers approving warrants for intrusive surveillance, and said there needed to be a compelling case for any extensions of powers.