BRITAIN'S intelligence agencies practise and uphold UK law at all times and claims they have used US intelligence to circumvent it are baseless, William Hague has insisted.

In a Commons statement, the Foreign Secretary sought to allay concerns that GCHQ, the UK Government's listening centre, had used data from America's Prism surveillance network.

He also said the UK's system of legal requirements and robust scrutiny, coupled with parliamentary oversight, was "one of the strongest systems of checks and balances and democratic accountability for secret intelligence anywhere in the world".

He described the US/UK intelligence relationship as unique and said it had saved many lives by stopping terrorist and espionage plots.

The Foreign Secretary said the importance of the relationship was most marked in the run-up to the 2012 Olympics.

He said: "The House will not be surprised our activity to counter terrorism intensified and rose to a peak in the summer of last year."

He also pointed out that the security services had frustrated terrorist attacks, "some of which we cannot talk about, which are not known to the public".

Prism is said to give America's National Security Agency (NSA) and FBI easy access to the systems of nine of the world's top internet companies, including Google, Facebook, Microsoft, Apple, Yahoo and Skype.

The row spread to the UK after documents emerged suggesting GCHQ had had access to the system since June 2010 at latest.

The leak came from Edward Snowden, 29, a computer administrator who worked for the NSA and the CIA.

At Westminster, Douglas Alexander for Labour insisted everyone had an interest in sustaining public confidence in the work of the intelligence agencies.

He asked Mr Hague to confirm they had to obtain legal authority to access emails of Britons, and whether the rules applied if they were to intercept the data or when another country did it for them.

The Foreign Secretary, who said he deplored the leak of classified documents but stopped short of commenting directly on Mr Snowden, ran through the process of obtaining permission for the security services to eavesdrop, which, he stressed, were governed by two acts of Parliament.

These require a signed warrant from the Foreign or Home Secretary, and must be "necessary, proportionate and carefully targeted". They are also subject to review by an independent commissioner to ensure permission is compliant with law.

Proposals have to be detailed, covering potential risks and intended benefits with comments from officials and lawyers.

Privacy is at the forefront of the minds of officials and ministers, insisted Mr Hague.

He added: "We take great care to balance individual privacy with our duty to safeguard the public and the UK's national security."

Labour backbencher Ann Clwyd, who has been in contact with US soldier Bradley Manning, who leaked documents to Wikileaks, sought reassurances her communications had not been intercepted.

Mr Hague replied by saying she could have confidence in the so-called Wilson Doctrine, which aims to prevent communications of MPs being monitored by intelligence or security officials.

Last night, Shami Chakrabarti, director of civil liberties campaign group Liberty, said: "He evaded specific questions as brazenly as his agencies have apparently avoided legal scrutiny and their embarrassment is now his.

"Reports to a secret committee are a start but the public won't be satisfied without greater honesty and legal protection from those who compromise our freedoms in freedom's name."