But there was a rule preventing USA from spying on the British citizens.
But that was changed in 2007 !
In 2007, the US and UK struck a deal allowing NSA to spy on Brits, even if they are not suspected of any wrongdoing.
To do that, England actually changed its rules.
In 2007, the rules were changed to allow the NSA to analyse and retain any British citizens' mobile phone and fax numbers, emails and IP addresses swept up by its dragnet. Previously, this data had been stripped out of NSA databases – "minimized", in intelligence agency parlance – under rules agreed between the two countries.
A separate draft memo, marked top-secret and dated from 2005, reveals a proposed NSA procedure for spying on the citizens of the UK and other Five-Eyes nations, even where the partner government has explicitly denied the US permission to do so. The memo makes clear that partner countries must not be informed about this surveillance, or even the procedure itself.
A spokeswoman for the NSA declined to answer questions from the Guardian on whether the draft directive had been implemented and, if so, when.
The NSA and the White House also refused to comment on the agency's 2007 agreement with the UK to store and analyze data on British citizens.