LONDON (Reuters) - Revelations by Edward Snowden about British eavesdropping are a gift to terrorists because they weaken the ability of the security services to stop those plotting deadly attacks against the West, the head of the MI5 Security Service said on Tuesday.
In an unusually frank public intervention in the debate over the powers of U.S. and British spy agencies, MI5 Director General Andrew Parker warned that his agents needed to read and listen to suspect communications to foil major attacks.
The extent of U.S. and British surveillance was laid bare in media reports based on previously top secret documents stolen by U.S. National Security Agency contractor Snowden, prompting a spy scandal that pitted Barack Obama against the Kremlin and triggered calls for greater scrutiny of Western agents.
Cautioning against complacency over the threat from militants, especially those returning from the battlefields of Syria, Parker dismissed as nonsense the idea that British spies gratuitously rummaged through private data of the innocent like the secret police of Communist East Germany or North Korea.
Though he did not mention Snowden by name, Parker warned about the danger of disclosures about the work of Britain's listening agency, known as GCHQ, whose capabilities were made public by media reports based on documents from Snowden stole.
"It causes enormous damage to make public the reach and limits of GCHQ techniques. Such information hands the advantage to the terrorists. It is the gift they need to evade us and strike at will," Parker said in his first public speech taking up his post as MI5 chief on April 22.
"The idea that we either can or would want to operate intensive scrutiny of thousands is fanciful. This is not East Germany, or North Korea. And thank goodness it's not," he told an audience in London.
The rare public intervention by one of the world's most senior spies indicates the level of concern within Britain's security services about the damage done by Snowden's revelations on both public perceptions and intelligence capabilities.
Snowden received temporary asylum in Russia in August.
In a clear attempt to nudge politicians towards legislation that would allow greater monitoring of communications, Parker said the changes in electronic communication could erode MI5's ability to stop trouble.
"We cannot work without tools," Parker said.
Just weeks after taking up his post in April as MI5 chief, Parker had to deal with both the Snowden revelations and the fallout from the killing of a 25-year-old British soldier on a London street.
Parker, who led MI5's response to the 2005 attacks on London which killed 52 civilians, said the threat from al Qaeda had become more unpredictable and complicated both in terms of country of origin and tactics.
"A time-lapse sequence of a world map over the past decade would show outbreaks in Iraq, North and West Africa, Yemen, Somalia, and most recently Syria," Parker said.
Syria, he said, was of particular concern. The worry is that impressionable British citizens could be radicalised by Islamist groups such as Al Nusra and then return from Syria to attack.
"A growing proportion of our casework now has some link to Syria, mostly concerning individuals from the UK who have travelled to fight there or who aspire to do so," Parker said.
"Al Nusra and other extremist Sunni groups there aligned with al Qaeda aspire to attack Western countries."
Parker said Britain had seen serious attempts at major attacks once or twice a year annually since 2000. He said that was unlikely to change.
"I do not believe the terrorist threat is worse now than before. But it is more diffuse. More complicated. More unpredictable."
Writing by Guy Faulconbridge; Editing by Angus MacSwan