Plans to expand the powers of the intelligence agencies to spy on emails and phone calls would break the coalition agreement, former Lib Dem leader Lord Ashdown has said.
Under legislation expected in next month's Queen's Speech, internet companies will be instructed to install hardware enabling GCHQ - the government's electronic "listening" agency - to examine "on demand" any phone call made, text message and email sent, and website accessed in "real time" without a warrant.
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, as well as civil liberties groups.
Internal coalition tensions over the plans were exposed this week after David Cameron said Nick Clegg as well as other senior Lib Dems had been present when the plans were agreed on.
However Clegg said his party would only support the measures if safeguards ensured civil liberties were protected.
Writing in The Times on Thursday, Lord Ashdown said the plans were more suited to regimes such as China, Russia or "some South American dictatorship" rather than Britain, and if enacted they would breach the coalition agreement signed by the Lib Dems and Tories that forms the basis of their power-sharing agreement.
"Liberals accept, subject to safeguards decided by parliament, that the government has a right to intercept the private communications of its citizens where it is necessary for national security and in the pursuit of serious crime, and that these powers should keep pace with the development of communications," he said.
"Any extension of these powers should be strictly proportionate to the threat. That is why we opposed the Labour Government when it tried to establish a central database in 2008.
"We have always resisted a ‘fishing trip’ approach by the security services, where they seek the right to gather information on innocent citizens merely on the ground that there may be some among them who are committing serious crime.
"The government’s new proposals to extend the retention of e-mail, social media, websites and internet phone records breach these basic principles; they are disproportionate and seek a generalised extension of state monitoring that applies to everyone, rather than to individuals."
Lord Ashdown said it was a basic right as "free citizens" to be able to "talk to whom we wish, when we wish and wherever we wish without the state knowing about it, unless there is good cause for it to do so".
"It is not just the content of our communication that is private. It is the fact that it occurred at all, when and for how long," he said.
"The 'content' cannot be separated from the context. For this reason it is difficult to see how these proposals do not run counter to the coalition agreement, which states: 'We will end the storage of e-mail and internet records without good reason'."
A history of the rise of the surveillance state over the past decade: