Under daily observation from thousands of surveillance cameras mounted everywhere from street corners to taxicabs to public parks, Britons rank among the most-watched people on Earth. But a new government plan is poised to take the gaze of this nation’s security services dramatically deeper: letting them examine the text messages, phone calls, e-mails and Web browsing habits of every person in the country.

The “snooping” proposal set to be presented in Parliament later this year is sparking an uproar over privacy in Britain, fueling a debate over the lengths to which intelligence agencies should go in monitoring citizens — a debate that has resonance on both sides of the Atlantic.

Government officials say the new powers are critical to countering terrorism and other threats in an era of fast-changing social media, with criminals using even seemingly innocent venues such as Facebook and online games as means of communication. But furious citizen groups and some members of Parliament see the push as a part of Britain’s evolution into a “surveillance society” in the aftermath of the Sept. 11, 2001, attacks in the United States and the 2005 London bombings.

Broad scope

Although the plan is yet to be fully outlined by the Conservative-led government, observers say parts of it may go beyond even the ability of officials in the United States to quickly access private data. Critics say the sheer breadth and scope of the plan also could put Britain out in front of other European countries such as Germany, where the government acts to block some Web sites deemed objectionable, and Sweden, where a law passed in 2008 allows the government to intercept international communications conducted via phones or the Internet.

“I’m afraid that if this program gets introduced, the U.K. will be leapfrogging Iran in the business of surveilling its citizens,” said Eric King, head of research at Privacy International. “This program is so broad that no other country has even yet to try it, and I am dumbfounded they are even considering it here.”

The plan may authorize the national surveillance agency — which is known as GCHQ and whose Web site describes its mission as keeping “our society safe and successful in the Internet age” — to order the installation of thousands of devices linked to the networks of Internet service providers, giving agents broader access to everyday communications. The examination of the contents of those exchanges — such as the text or images contained in an e-mail — would still require special warrants.

But for the first time, intelligence agencies might, for instance, access information such as the times, destinations and frequencies of phone calls, texts and e-mails without a warrant. They could also use collected data to track worrisome Internet patterns in a bid to expose terrorist cells, pedophilia rings and other lawbreakers, according to sources briefed on the proposal, which came to light after a report this weekend in London’s Sunday Times.

The measure reportedly would compel communications companies to grant intelligence agents instant access to real-time information in certain circumstances, such as data that could be used to target the location of a user’s mobile phone or computer if authorities suspected a crime was in progress. It remained unclear whether British authorities would need judicial or other authority before accessing such data.

“It is vital that police and security services are able to obtain communications data in certain circumstances to investigate serious crime and terrorism and to protect the public,” Britain’s Home Office — a rough equivalent to the U.S. Department of Homeland Security — said in a statement.

‘A dangerous trend’

Privacy advocates reacted swiftly Monday, saying the move would intrude so deeply into the lives of British citizens that it would rival or exceed measures used by totalitarian governments. They say it marks another of many steps that have curtailed privacy rights here in the post-Sept. 11 world, with one study by British police officials, for instance, indicating that a person strolling around London is captured on film by at least 68 cameras on any given day.

Still, details of the proposal have not been disclosed, and some experts say it could yet be weakened. But as it stands, key aspects of the proposal may go beyond the kind of surveillance now authorized in the United States, where privacy advocates were quick to raise concerns about the plan — especially given the heavy traffic of transatlantic communication.

“It’s a dangerous trend to have this level of surveillance being made a routine matter,” said Lee Tien, senior staff attorney with the San Francisco-based Electronic Frontier Foundation.

Access in the United States to “metadata” — such as the time, who e-mailed whom and how often — depends on the kind of data and type of case. For example, authorities have to obtain court orders before accessing real-time data in both criminal and national security cases.

In criminal cases, authorities need a subpoena to get stored metadata on phone numbers dialed but a court order for e-mail information. In contrast, federal agents seeking stored e-mail header information in national security cases have contended that they may use a national security letter, which is an administrative subpoena that can be issued by an FBI field office. But some providers have refused access to such data without a court order.

Britain generates more than 2 million e-mails a minute, and observers say the government may face technical challenges in capturing and storing such vast amounts of data. Currently, firms are required to store some communications data, such as phone calls, for one year. But the proposed law could compel them to store far more varied forms — such as Skype calls or online video game data — for at least twice as long.

Internet companies reacted cautiously Monday, saying they needed to see the full proposal. “It is important that proposals to update government capabilities to intercept and retain communications data are proportionate, respect freedom of expression and the privacy of users,” Britain’s Internet Service Providers Association said in a statement.

Government officials on Monday sought to calm the growing public backlash, which includes at least two petitions against the measure. Nick Clegg, the deputy prime minister, said the proposal makes a sharp distinction between monitoring details such as the frequency and times of phone calls and e-mails and accessing their contents.

“I am totally opposed to the idea of governments reading people’s e-mails at will or creating a new central government database,” Clegg said. “All we are doing is updating the rules which currently apply to mobile telephone calls, to allow the police and security services to go after terrorists and serious criminals and updating that to apply to technology like Skype, which is increasingly being used by people who want to make those calls and send those e-mails.”

Yet observers note that the Conservative Party and the Liberal Democrats, who make up Britain’s coalition government, strongly opposed a similar plan briefly floated by Tony Blair’s Labor government in 2006. David Davis, a Conservative lawmaker and outspoken critic of the new proposal, said the shift appears to have come about because of pressure from high-ranking members of Britain’s intelligence agencies, who see the new powers as pivotal.

“They are talking about doing this with no real judicial control,” Davis said. “If they seek this information after a judge’s warrant, I would be perfectly happy. But this is unfettered access. This kind of data mining can lead to innocent people being pursued.”

Special correspondent Karla Adam in London contributed to this report.