Deputy PM says Edward Snowden revelations are 'chipping away at bedrock of public support for work of agencies'

Nick Clegg has hinted at the need for a wider inquiry into the "unimaginable" power of spying technology as US whistleblower Edward Snowden's leaks are chipping away at public support for the intelligence agencies.

The deputy prime minister said there was a stronger and stronger case for a broad inquiry with each passing day of revelations about the scale of mass surveillance by British and US security services.

In his strongest comments yet, Clegg said a new inquiry could look at the proportionality of surveillance on top of existing oversight by the intelligence and security committee and judges.

Asked about new reports in the Guardian about US spying on British internet users, Clegg said: "The technologies which are now used by our security agencies are far, far more powerful and are able to store and analyse data on a scale we have never known before.

"The ability now to hoover up, analyse, discard, process information is now on a scale which was unimaginable even a few years ago. So I think it is right to ask questions about the proportionality of modern intelligence-gathering and use of data and, crucially, the accountability."

Speaking on his LBC 97.3 radio show, Clegg said he strongly supported the need for secrecy by the intelligence agencies but there needed to be proper accountability as current regulation was quite opaque.

"Unless there is proper accountability, it is not legitimate in the eyes of the public," he said. "Frankly, I think we can and should reflect on what more we can do.

"I do think there is a legitimate question to ask, which is: how do you make sure you have proper accountability and proper proportionality about the use of these powers?

"With each passing day with all of these revelations you chip away at the bedrock of public support for the work of the agencies and that is a dangerous thing."

He suggested there could be a review similar to that set up in the US by Barack Obama, and did not dismiss the idea of a public inquiry.

"We have these arrangements in place – the intelligence and security committee, they are doing a review, you have these judges to test these agencies."

But he said "with each passing day there is a stronger and stronger case to look at this in the round" and added he had an "open mind on how to try and keep up with all these different issues so we keep up with the revolution in the power of intelligence agencies and are open to those who want to do us harm".

Clegg's comments come after several senior Liberal Democrats, including former leader Lord Ashdown, said more must be done to investigate the scale of internet surveillance by spies.

David Cameron and the heads of the intelligence agencies have claimed the Guardian endangered national security by publishing stories based on Snowden's leaks.

Andrew Parker, the head of MI5, said the stories were a "gift" to terrorists, while Tory MP Julian Smith has called for the Guardian to be prosecuted over the way it has stored and transported files.

Police detained David Miranda, the partner of then Guardian journalist Glenn Greenwald, under terrorism laws and mounted an investigation after seizing documents.

However, there have been growing calls from politicians for more scrutiny of the intelligence services as more emerges from the Snowden files.

There has been international outrage about reports the US tapped the phones of 35 world leaders and the power of the NSA and GCHQ to secretly access undersea internet cables carrying the communications of millions of users.

The intelligence and security committee is now looking at oversight of the agencies, whose heads gave evidence in public for the first time a few weeks ago.

However, Clegg's comments will increase pressure for a more independent investigation.