Britain's spying bosses did not use a controversial US surveillance programme to dodge UK laws, according to a parliamentary committee.
GCHQ had been accused of using the Prism programme, which sparked outrage when details were leaked last month, to circumvent strict controls.
But the Intelligence and Security Committee, which oversees the work of the intelligence agencies, said it was satisfied that GCHQ had conformed with its statutory duties.
Civil liberties campaigners gave a sceptical reaction, branding the committee's findings a "whitewash".
According to the committee, in each case where GCHQ sought information from the US, an intercept warrant signed by a minister was already in place.
It follows allegations based on disclosures by US whistleblower Edward Snowden that GCHQ used the American National Security Agency's Prism programme to access material from the leading internet companies.
"It has been alleged that GCHQ circumvented UK law by using the NSA's Prism programme to access the content of private communications. From the evidence we have seen, we have concluded that this is unfounded," the committee said.
Foreign Secretary William Hague welcomed the committee's findings.
"I see daily evidence of the integrity and high standards of the men and women of GCHQ. The ISC's findings are further testament to their professionalism and values," he said.
"The Intelligence and Security Committee is a vital part of the strong framework of democratic accountability and oversight governing the use of secret intelligence in the UK.
"It will continue to have the full co-operation of the Government and the security and intelligence agencies."
Shami Chakrabarti, director of civil rights group Liberty, said the committee's findings would do little to reassure people that their data was not being improperly accessed.
"The painfully careful words of the ICS's report clean absolutely nothing up," she said.
Nick Pickles, of the Big Brother Watch campaign group, said Parliament needed to act urgently to ensure the legal framework was fit for the needs of the internet age.