British intelligence agencies have broken no laws and are subject to "proper" parliamentary scrutiny, Prime Minister David Cameron insisted today as the NSA PRISM scandal reached Blighty.

He was forced to defend Brit spooks following allegations that UK eavesdropping nerve-centre GCHQ had access to the Americans' controversial PRISM project, which gathers emails, chat logs and other private information about folks from internet giants. It is alleged such access allowed GCHQ to circumvent the law, avoid ministerial scrutiny and sidestep the need to obtain a court order when snooping on people.

The claims were made late last week by ex-CIA techie Edward Snowden.

The allegations led to the chairman of Parliament's Intelligence and Security Committee, Malcolm Rifkind, hastily announcing before the weekend that his panel of MPs expect a full report from GCHQ about PRISM imminently.

He said that the committee would "decide what further action needs to be taken as soon as it receives that information".

At lunchtime today, meanwhile, the PM insisted that UK spooks "operate within the law". His defensive remarks came after a difficult weekend for the US government as it attempted to shrug off Snowden's leak by downplaying PRISM's significance: officials said there were inaccuracies in news reports about the programme and that the project was being used to target foreigners rather than American citizens.

President Barack Obama - who appeared to have widened the scope of internet surveillance after PRISM was brought in by his predecessor George W Bush in 2007 - characterised the web-snooping programme as a "modest encroachment" on individuals' privacy.

Cameron declined today to comment on what he knew about PRISM, prior to Snowden's leak.

"Let us be clear. We cannot give a running commentary on the intelligence services," the prime minister said. "I am satisfied that the intelligence services, who do a fantastically important job to keep us safe, operate within the law and within a legal framework and they also operate within a proper framework of scrutiny by the intelligence and security committee."

He added: "We do live in a dangerous world and live in a world of terror and terrorism. I do think it is right we have well-funded and well-organised intelligence services to keep us safe."

Home Secretary Theresa May, who has fought to secure more internet snooping powers for Britain's security services with her failed Communications Data Bill, told MPs this afternoon that "at all times GCHQ has operated within a fully legal framework", but added that she welcomed the intelligence committee's urgent probing of PRISM.

Committee chairman Rifkind told BBC's Radio 4 that the current law about intercepting communications was "quite clear".

"If the British intelligence agencies are seeking to know the content of emails about people living in the United Kingdom, then they have to get authority. That means ministerial authority," he said.

UK Foreign Secretary William Hague said on Sunday that law-abiding Brits had "nothing to fear".

And he told the House of Commons that "the [British] government deplores the leaking of any classified information wherever it occurs" and added that "to intercept content of any individual’s communications in the UK requires a warrant signed by me or the Home Secretary".

He further insisted "any data obtained by us from the US involving UK nationals is subject to proper UK statutory controls and safeguards", adding that accusations of GCHQ circumventing UK law by using the PRISM spy programme were "baseless". ®