LONDON (Reuters) - Britain's terrorism law watchdog called on Thursday for a major overhaul of the framework governing the use of mass surveillance, posing a potential challenge to the government in its bid to hand more powers to police and spies.
David Anderson, Britain's independent reviewer of anti-terrorism laws, said the government needed to spell out why intrusive powers were needed.
New safeguards were required and further powers should only be allowed after a detailed examination of their lawfulness and effectiveness, he added.
"Each intrusive power must be shown to be necessary, clearly spelled out in law, limited in accordance with international human rights standards and subject to demanding and visible safeguards," said Anderson in a 373-page report for Prime Minister David Cameron on intrusive investigation tactics.
Cameron, fresh from an election victory last month, has promised a swathe of new security measures, the most striking and controversial of which are plans to give police greater powers to monitor Britons' communications and web activities in what opponents have called a "snoopers' charter".
He and security chiefs argue these are needed if the authorities are to keep up with technological advances and so are vital to preventing attacks, warning that Britain was facing an unprecedented threat from groups such as Islamic State.
But in his report, Anderson said extending current powers should not happen without great justification.
"There should be no question of progressing proposals for the compulsory retention of third-party data before a compelling operational case has been made out (as it has not been to date) and the legal and technical issues have been fully bottomed out," he said in his report.
(Reporting by Michael Holden; editing by Stephen Addison)