The Liberal Democrats have pledged to end the "Orwellian nightmare" of mass-snooping powers in the Investigatory Powers Act ahead of their manifesto launch.
They will propose to roll back state surveillance powers by ending the indiscriminate bulk collection of communications data and internet connection records.
The party also committed to fighting Conservative attempts to undermine encryption, which it warned will put people's online security at risk.
It comes as a recent leaked draft document from the Home Office has revealed that government aims to be able to access anyone's communications within 24 hours and to bring an end to encrypted messages under the recently passed Investigatory Powers Bill.
Under the plans, companies would be legally required to introduce a backdoor to their systems so authorities can read all correspondence if required.
Labour's leaked manifesto did not mention the subject of government mass surveillance.
The Lib Dems have long been against the legislation. However, the party currently has just nine MPs, one of whom, Alistair Carmichael, said the legislation has laid the ground for a "full frontal assault" on privacy and civil liberties.
"The security services need to be able to keep people safe, but these powers are straight out of an Orwellian nightmare. They have no place in an open and democratic society, will cost billions of taxpayers' money and simply will not work.
"Instead of spying on the entire population's web histories and undermining the encryption that, for example, allows us to bank online safely, Liberal Democrats would put money back into community policing and concentrate on intelligence-led, targeted surveillance." ®