Police and security services have been granted new powers to hack into personal computers without a warrant, following European Union proposals aimed at extending the use of intrusive surveillance.
They allow the use of keyloggers, which can be installed in a variety of ways, to monitor keyboard use including emails, web surfing and instant messaging conversations.
Authority must still be obtained from a chief constable, but the new measures have angered opposition MP's, and civil liberty and privacy organizations are threatening a legal challenge.
"The exercise of such intrusive powers raises serious privacy issue," said Shadow Home Secretary Dominic Grieve. "The government must explain how it would work in practice and what safeguards will be in place."
Shami Chakrabati, director of human rights group Liberty, added: "These are very intrusive power. The public will want this to be controlled by new legislation and judical authorization.
"Without those safeguards it is a devastating blow to any notion of personal privacy. This is no different from breaking down someone's door, rifling through their paperwork and seizing their computer hard drive."
The Association of Chief Police Officers (ACPO) defended the move, pointing out that it would still be governed by the Regulation of investigatory Powers Act.
According to the police, 194 police hacking operations were carried out in England, Wales and Northem Ireland over the past two years: 133 in private homes, 37 in offices and 24 i hotels.