Foreign Secretary William Hague and Prime Minister David Cameron have both sought to defend the work of GCHQ in the wake of the PRISM scandal, by insisting the listening post complies with UK law at all times.
In a statement made to the House of Commons, Hague said GCHQ and the American National Security Agency (NSA) "have ... a relationship that is unique in the world".
However, he contended that suggestions GCHQ uses this partnership to get around UK law were "baseless".
"Any data obtained by us from the US involving UK nationals is subject to proper UK statutory controls and safeguards, including the relevant sections of the Intelligence Services Act, the Human Rights Act and the Regulation of Investigatory Powers Act (RIPA)," said Hague.
"Our Intelligence Agencies practise and uphold UK laws at all times, even when dealing with information from outside the UK," he added.
Hague also said the Government "deplores the leaking of any classified information", but would neither confirm nor deny any aspect of the leaked information.
Speaking at a separate press conference, David Cameron said the UK intelligence services operate "within the law ... and they are also subject to proper scrutiny by the Intelligence and Security committee in the House of Commons ... and I'll always make sure that it takes place".
He also refused to be drawn into speculation on PRISM.
Despite these reassurances, privacy campaigners have said there are still questions to answer over the UK's involvement in the US' electronic surveillance programme.
Jim Killock, executive director of the Open Rights Group, said Hague did not answer crucial questions from several MPs regarding the use of UK citizens' data by the US intelligence services.
"Hague gave no reassurances about what the USA is doing with UK citizens' information. In the USA, we have no right to privacy, as non-US citizens," said Killock.
"If Hague was hoping to reassure the British public, he singularly failed to do so," he added.
