Theresa May has defended government proposals to monitor all calls, emails, texts and website visits, saying the new powers will be vital in catching terrorists, paedophiles and serious criminals.
The Home Secretary insisted that ordinary people will not be targeted as she sought to quell fears about the plans which have faced fierce criticism from backbench MPs and civil liberties groups.
The legislation, expected in next month's Queen's Speech, will enable GCHQ to access information "on demand" in "real time" without a warrant.
Writing in The Sun, Ms May said the proposed law change, which will mean internet companies are instructed to install hardware tracking telephone and website traffic, would help police stay one step ahead of criminals.
"The Internet is now part of our daily lives, but new technology can also be abused by criminals, paedophiles and terrorists who want to cover their tracks and keep their communication secret," she said.
"Right now, the police and security agencies use information from phone records to solve crime and keep us safe. Looking at who a suspect talks to can lead the police to other criminals. Whole paedophile rings, criminals conspiracies and terrorist plots can then be smashed."
Ms May said the monitoring techniques had helped put murderer Ian Huntley and the killers of Rhys Jones behind bars and also smashed an internet child pornography website based in Lincolnshire last year.
She added: "We cannot afford to lose this vital law enforcement tool. But currently online communication by criminals can't always be tracked. That's why the Government is proposing to help the police stay one step ahead of the criminals.
"There are no plans for any big Government database. No one is going to be looking through ordinary people's emails or Facebook posts. Only suspected terrorists, paedophiles or serious criminals will be investigated."
Information Commissioner Christopher Graham has said the watchdog will press for "limitations and safeguards" to protect citizens' privacy if the proposals are introduced.
Downing Street insisted only data - times, dates, numbers and addresses - not content would be accessible.
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.
David Davis, Conservative former shadow home secretary had said the law change is not necessary.
"What is proposed is completely unfettered access to every single communication you make," he said.
Civil liberty campaign group Liberty and the Big Brother Watch campaign group have also slammed the proposals, describing them as "chilling" and a "unprecedented intrusion" into the lives of UK citizens respectively.