Plans to massively expand powers to snoop on email and other online communications have provoked a storm of protest from civil liberties campaigners.Under the move, internet companies would be instructed to install hardware that would allow spycentre GCHQ to examine "on demand" communications judged by the Home Office to be suspect.
GCHQ would need a warrant to access the content of communications but would be able to trace who people are in touch with and how often and how long they are in contact.
Ministers believe it is an essential step to help police and security services combat terrorism and protect the public. Legislation on the issue is expected to be in the Queen's Speech.
The Home Office said: "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.
"We need to take action to maintain the continued availability of communications data as technology changes. We will legislate as soon as parliamentary time allows to ensure that the use of communications data is compatible with the Government's approach to civil liberties."
This is an unnecessary extension of the ability of the state to snoop on ordinary innocent people in vast numbers. Frankly, [the government] shouldn't have that power.
David Davis MP, former Tory leadership challenger
A similar scheme floated by the then Labour government six years ago was dubbed "the Big Brother bill", and abandoned in the face of fierce Tory and Lib Dem opposition.
Shami Chakrabarti, director of the civil rights group Liberty, said: "There is an element of whoever you vote for the empire strikes back.
"This is more ambitious than anything that has been done before. It is a pretty drastic step in a democracy."
Nick Pickles, director of the Big Brother Watch campaign group, added: "This is an unprecedented step that will see Britain adopt the same kind of surveillance seen in China and Iran."
The bill will also face some resistance from some Conservative MPs.
Former party leadership campaigner David Davis said: "This is an unnecessary extension of the ability of the state to snoop on ordinary innocent people in vast numbers. Frankly, they shouldn't have that power."
And backbench Tory MP Margot James predicted that the law would not get an easy passage through parliament.
"I am sure there will be considerable pressure brought to bear as the proposals are debated for protections to be built in to protect people's privacy," she told Sky News.
There are also concerns among internet providers, who will have to install thousands of pieces of hardware to make the state-sponsored eavesdropping possible.
However, in a sense the concept itself is nothing new.
In 1655, the Post Office was put under the direct control of John Thurloe - a man best known to history as Oliver Cromwell's spymaster general.
Previous English governments had tried to prevent conspirators communicating but the technique Thurloe adopted was to deliver the post, after having secretly read it first.