Former US secretary of state Hillary Clinton has called for a "sensible adult conversation" about the boundaries of state surveillance following the leaking of secret files by whistleblower Edward Snowden.
Mrs Clinton said it would be "going down a wrong path" to reject a debate in the wake of disclosures about the collection of communications data by America's National Security Agency (NSA) and the Government's secret eavesdropping station GCHQ.
Speaking at Chatham House in London, where she collected a prize for her contribution to international diplomacy, Mrs Clinton told the Guardian: " This is a very important question. On the intelligence issue, we are democracies thank goodness, both the US and the UK.
"We need to have a sensible adult conversation about what is necessary to be done, and how to do it, in a way that is as transparent as it can be, with as much oversight and citizens' understanding as there can be."
Mrs Clinton, who is considering whether to make her second challenge for the Democratic presidential nomination in 2016, added: "It would be going down a wrong path if we were to reject the importance of the debate, and the kinds of intelligence activities that genuinely keep us safe.
"So how do we sort all of this out? This is a problem that is well over a decade old, where these capacities have corresponded with increasing outreach to consumers on the business side and increasing concern about security on the government side. People need to be better informed."
But the Prime Minister's spokesman said there was no official Government review and Mr Cameron believed the current system works well.
Mr Cable called for "proper political oversight" of the intelligence services and said the Guardian newspaper had performed "a very considerable public service" in publishing secret material leaked by Mr Snowden, which revealed the extent of mass surveillance programmes operated by the NSA and Cheltenham-based GCHQ.
But a senior Whitehall security expert said that the Snowden leaks amounted to the "most catastrophic loss to British intelligence ever".
Sir David Omand, the former head of GCHQ who was once homeland security adviser to Number 10, said the leak of tens of thousands of files by the former US intelligence operative eclipsed the Cambridge spy ring, which saw five university students recruited as Soviet spies.
Earlier this week, MI5 head Andrew Parker warned that the Snowden leaks were a "gift" to terrorists, by exposing the ''reach and limits'' of the GCHQ listening post. His comments sparked criticism in some quarters of the Guardian's decision to give Snowden publicity.
But Mr Cable defended the newspaper, telling BBC Radio 4's Today programme yesterday: "I think The Guardian has done a very considerable public service. I think Mr Snowden's contribution is twofold, one of which is a positive one - which is whistle-blowing - and the other of which is more worrying, that a large amount of genuinely important intelligence material does seem to have been passed across.
"The conclusion that Nick Clegg came to and set out this morning is that we do need to have proper political oversight of the intelligence service and arguably we haven' t done until now.
"What they did as journalists was entirely correct and right. Mr Snowden is a different kettle of fish."
Earlier this week Mr Cameron said: "If people want to suggest improvements I am very happy to listen to those, but as far as I can see we have a very good system."
His spokesman said: "It is open, of course, to anyone on the National Security Council to go and speak to the agencies, discuss with them, ask questions about what they do. Of course that is open to anyone on the National Security Council, in fact any privy councillor."
But he stressed: "There is not a Government review."
Aides to the Deputy Prime Minister told the Guardian that Mr Clegg is considering how to update the legal oversight of Britain's security services and would be calling on experts to discuss the implications of new surveillance technologies for public accountability and trust.
Mr Snowden, who is in Russia, leaked information to the Guardian in May that revealed mass surveillance programmes such as the NSA-run Prism and GCHQ's Tempora.
Under the £1 billion Tempora operation, GCHQ is understood to have secretly accessed fibre-optic cables carrying huge amounts of internet and communications data and shared the information with the NSA.
A senior government minister called for cabinet colleagues to give "very, very robust" support to GCHQ workers.
"In the aftermath of Snowden they have been very exposed and I think it is really important that in those circumstances that ministers involved should give very, very robust support to them and acknowledge what an incredibly important work they do," Mr Maude told the audience.
"So many civil servants do a fantastic job often in really difficult circumstances."