The US government paid Britain’s spying centre at GCHQ £100m over three years, according to documents leaked by whistleblower Edward Snowden.
According to the Guardian newspaper, the payments were made in order to secure access to Britain's intelligence gathering programmes.
In return for the payment GCHQ was required to ‘pull its weight’, according to the documents which were leaked last night.
The newspaper claims the payments were set out in papers which made clear that the Americans expected a return on the investment.
"GCHQ must pull its weight and be seen to pull its weight," a strategy briefing by the electronic listening post said.
In a 2010 document the Cheltenham-based agency acknowledged that the US had "raised a number of issues with regards to meeting NSA's minimum expectations" and GCHQ "still remains short of the full NSA ask".
In the documents GCHQ describes Britain's surveillance laws and regulatory regime as a "selling point" for the Americans, the newspaper claimed.
Shadow foreign secretary Douglas Alexander said: "The vital work of the intelligence agencies requires effective and thorough oversight by the Intelligence and Security Committee on behalf of Parliament, and by ministers, and in the case of GCHQ, by the Foreign Secretary.
"The latest reports in the Guardian only underline the importance of the Foreign Secretary and the Intelligence and Security Committee being able to assure the public that the legal framework within which our intelligence agencies operate is both being adhered to and is fit for purpose."
The information is the latest to be leaked by Mr Snowden, a former NSA contractor who was charged with espionage in the US.
Yesterday, Mr Snowden was allowed to leave Moscow’s Sheremetyevo Airport, where he has been since late June after exposing the NSA's use of an intelligence programme, known as PRISM, to spy on Facebook accounts, emails and phone calls.
He was granted temporary asylum in Russia on the proviso that he would not publish any further documents that blacken the American government.
The Russian move is likely to further aggravate relations with the United States that were already strained by support for Syrian President Bashar al-Assad in that country's bloody civil war and a host of other issues.
"We see this as an unfortunate development and we are extremely disappointed by it," White House spokesman Jay Carney told reporters in Washington.
"We are evaluating the utility of a summit, in light of this and other issues, but I have no announcement today on that.
Additional reporting by ReutersReuse content