MI6 chief Sir John Sawers said al-Qaeda were “rubbing their hands with glee” at the exposure of the surveillance methods used by GCHQ – Britain’s electronic eavesdropping agency – and its US counterpart, the National Security Agency.
Sir Iain Lobban, the director of GCHQ, said that in the five months since Mr Snowden’s revelations started appearing in the media, they had monitored terrorist groups discussing in “specific terms” how to avoid communications systems they now considered to be vulnerable.
In a 90-minute hearing at Westminster, the spy chiefs insisted they operated at all times within the framework of the law and did not engage in mass “snooping” on ordinary citizens.
They made plain their anger at the damage they said had been done to national security as a result of Mr Snowden’s leaks.
Sir Iain suggested the leaks could help serious criminals and even paedophiles avoid detection, as the success of surveillance operations depended upon the targets being “unaware or uncertain” of the methods being used against them.
When those methods were made public, the effect, he said, could be a “sudden darkening” of the intelligence picture.
“More often, it is gradual, but it is inexorable. What we have seen over the last five months is near daily discussion amongst some of our targets,” he said.
“We’ve seen terrorist groups in the Middle East, in Afghanistan and elsewhere in south Asia discussing the revelations in specific terms, in terms of the communications packages that they use, the communications packages that they wish to move to.
“We have actually seen chat around specific groups, including closer to home, discussing how to avoid what they now perceive to be vulnerable communications methods, or how to select communications which they now perceive not to be exploitable.”
Asked whether the discussions related directly to recent revelations about surveillance, Sir Iain said: “It is a direct consequence. I can say that explicitly.”
Sir John said the leaks had been “very damaging”, putting operations at risk and making it more difficult to recruit agents in dangerous situations abroad.
“It is clear that our adversaries are rubbing their hands with glee, al-Qaeda is lapping it up,” he said. “We’ve an extraordinarily difficult task. We have to identify and recruit agents in the most exposed places – in the higher reaches of al-Qaeda, in the countries that are trying to do our country harm, secret states that are trying to do damage to us.
“We need to have the possibility of examining the intelligence, of drawing information that our partner agencies have, in order to identify those very brave individuals that are prepared to work with us against their undemocratic, secretive, oppressive societies which cause us threat. If you end up diminishing our ability to use technology, we will be less able to have that advantage we have and our country will be less safe.”
Mr Parker said MI5 relied heavily on GCHQ’s ability to intercept terrorist communications to disrupt plots in the UK. “The advantage that we have as intelligence agencies that leads to that sort of opportunity can be fragile, and if we lose it then we are just making a very difficult task even harder,” he said.
After the hearing, committee chairman Sir Malcolm Rifkind said Sir Iain had not mentioned in previous closed evidence that GCHQ had eavesdropped on terrorists discussing changing their methods. “That’s something that must have happened very recently, that they’ve got that hard evidence,” he said.
Sir Iain acknowledged there was an “active” discussion as to whether GCHQ could publicly say more about its operations, but he insisted it was not engaged in the mass monitoring of communications of ordinary citizens. “We do not spend our time listening to the telephone calls or reading the e-mails of the majority, the vast majority. That would not be proportionate, it would not be legal. We do not do it,” he said.