Christopher Graham, Information Commissioner for the UK, wants assurances about plans that will mean internet companies are instructed to install hardware tracking telephone and website traffic.
The legislation, expected in next month’s Queen’s Speech, will enable GCHQ to access information “on demand” in “real time” without a warrant.
A spokesman for the Information Commissioner’s Office said: “The Information Commissioner’s role in this Home Office project, both under this government and the last, has been to press for the necessary limitations and safeguards to mitigate the impact on citizens’ privacy.
“We will continue to seek assurances, including the implementation of the results of a thorough Privacy Impact Assessment [PIA].
“Ultimately, the decision as to whether to proceed with the project is one which has to be taken by parliament.”
Downing Street insisted only data – times, dates, numbers and addresses – not content would be accessible as it sought to quell fears about the proposals amid a fierce backlash from its own backbenchers as well as civil liberties groups.
A previous attempt to introduce a similar law was abandoned by the former Labour government in 2006 in the face of fierce opposition from the Conservatives and the Liberal Democrats.
Deputy Prime Minister Nick Clegg defended the plans, insisting he was “totally opposed” to the idea of governments reading people’s e-mails at will.
He added: “We are not doing any of that and I wouldn’t allow us to do any of that.
“I am totally opposed to it, as someone who believes in people’s privacy and civil liberties.”