A civil liberties group on Friday criticized new British rules that will require Internet service providers to keep records of every e-mail sent or received in the country for up to a year.
The rules, which come into effect by March 15, implement a 2006 European Union directive. Service providers will not store the content of e-mails, and the government says there is no threat to individual privacy.
But Shami Chakrabarti, director of the rights group Liberty, said she was worried the government would seek greater powers.
"The thing we have to worry about is what happens next because the government is already mooting plans not just to leave this stuff with the providers, but to create a central government database where they hold all the information," she told the BBC.
"I'm afraid we just don't trust any government or any organization to keep that much very sensitive information about us all and to keep it safe."
A Home Office spokeswoman, speaking on condition of anonymity in line with policy, said the data would enhance national security and help law-enforcement agencies conduct increasingly complex criminal and terrorist investigations.
But Richard Clayton, a security researcher at the University of Cambridge, said the plan was a waste of money.
"There's going to be a record of every single e-mail which arrived addressed to you and all the e-mails you sent out via your ISP," he told the BBC.
"That of course includes all the spam," Clayton said. "There are much better things to do to spend our billions on than snooping on everybody in the country just on the off chance that they're a criminal."
Trust in the government has been hit by a series of lost data incidents. In November, a government department lost a disk that contained the names, addresses and bank details of 25 million people.
Rights groups also worry that the government plans more sweeping communications powers. In October, Home Secretary Jacqui Smith said the government was considering setting up a database of all phone and e-mail traffic in the country as part of a high-tech strategy to fight terrorism and crime.
Opposition parties joined civil libertarians in criticizing the proposal, and the government said nothing would be done until after a public consultation this year.