National Security Agency whistle-blower Edward Snowden has claimed the UK spying agency can eavesdrop on people by controlling the microphones of their phones and even remotely switch the handsets off and on.
Talking to the BBC's Panorama programme, Snowden said the UK’s Government Security Headquarters has developed a set of tools, dubbed the smurfs after the popular Belgian cartoon characters, which it can efficiently use to eavesdrop on anyone.
"Dreamy Smurf is the power management tool which means turning your phone on and off without you knowing,” said Snowden, currently living in Russia since he sought temporary asylum there in June 2013.
"Nosey Smurf is the hot miking tool, so, for example, if it's in your pocket they can turn the microphone on and listen to everything that's going on around you."
There is also a third tool called the Tracker Smurf that allows GCHQ to monitor the movements of the user by closely tracking his or her phone. "They want to own your phone instead of you,” Snowden said.
The GCHQ said all its activities comply with European laws and the Convention on Human Rights.
"All of GCHQ's work is carried out in accordance with a strict legal and policy framework, which ensures that our activities are authorised, necessary and proportionate and that there is rigorous oversight, including from the Secretary of State, the Interception and Intelligence Services Commissioners and the Parliamentary Intelligence and Security Committee,” said the GCHQ spokesperson,
"All our operational processes rigorously support this position.”
The existence of the Smurf tools has previously been reported by Amnesty International.
In the Panaroma interview, Snowden said the GCHQ operated basically as a subsidiary of the American National Security Agency (NSA), whose large-scale eavesdropping programmes were in the centre of the revelations Snowden made in May 2013.
The GCHQ, Snowden said, is not only using the same technology as the NSA but also closely following its guidance.
The UK Government claimed in June that Britain had been forced to withdraw intelligence agents from operations because Russia and China had obtained access to secret information in files stolen by Snowden.
The leaking of tens of thousands of documents about surveillance programmes run by the NSA has been largely controversial with the FBI deputy director Mark Guiliano branding Snowden a traitor.
Snowden, a former NSA contractor, has been charged with violation of the US Espionage Act and theft of government property.
Snowden said he would be willing to return to the US to go to prison, but wouldn’t want to serve as a "deterrent to people trying to do the right thing in difficult situations."
"I have paid a price but I feel comfortable with the decisions I've made. If I'm gone tomorrow, I'm happy with what I had, I feel blessed," he said.
"The question is, if I was a traitor, who did I betray? I gave all of my information to American journalists and free society generally."