Powers for police to access internet records and hack into suspects' smartphones and computers are to be extended under revamped spying laws.
The Investigatory Powers Bill has been amended to allow law enforcement bodies to acquire data relating to people's web use for specific investigations.
Under the draft version of the proposed legislation access to internet connection records (ICRs) was limited to identifying the sender of a communication, the communications services a person was using, or determining whether an individual has accessed illegal material online.
The revised proposals presented in Parliament state that records should also be available for the pursuit of investigative leads if it is deemed "necessary and proportionate".
The move reflects a recommendation by a committee of peers and MPs.
Senior officers had argued that proposed rules around access to the data in the draft Bill unveiled in November appeared to preclude access to details that could be valuable in missing people inquiries and human trafficking investigations, such as travel bookings.
Firms will be required to store ICRs - which detail services a device connects to but not users' full browsing history or the content of a communication - for up to a year.
The circumstances for using equipment interference (EI) powers - which allow authorities to interfere with electronic equipment such as PCs and smartphones in order to obtain data - have also been adapted.
Now law enforcement agencies will be able to use these tactics in "threat to life" situations.
The original draft had restricted them to detecting or preventing serious crime, which the Government says would potentially prohibit police from using the tactics to save a life or locate a missing child.
The Bill states that a targeted EI warrant can be issued if it is considered necessary by a law enforcement chief for "the purpose of preventing death or any injury or damage to a person's physical or mental health or of mitigating any injury or damage to a person's physical or mental health".
Officials stressed EI warrants will be subject to "double lock" authorisation - meaning they must be signed off by a judge - and the most intrusive tactics will be restricted to a small number of forces and bodies.
Another change to the Bill will provide for a Secretary of State to authorise warrants for bulk EI by spy agencies in urgent circumstances, such as a foreign cyber-attack on UK infrastructure.
The methods are seen as increasingly crucial as advanced encryption makes it more difficult for security services to keep track of terrorists.
The Government has made a raft of revisions to the Bill, which aims to bring myriad surveillance powers under one legal umbrella, after three parliamentary inquiries raised concerns.
Home Secretary Theresa May said: "This is vital legislation and we are determined to get it right.
"The revised Bill we introduced today reflects the majority of the committee's recommendations - we have strengthened safeguards, enhanced privacy protections and bolstered oversight arrangements - and will now be examined by Parliament before passing into law by the end of 2016.
"Terrorists and criminals are operating online and we need to ensure the police and security services can keep pace with the modern world and continue to protect the British public from the many serious threats we face."
The Government said the revised Bill:
:: Is clearer, with "tighter definitions" and strict codes of practice.
:: Explicitly bans agencies from asking foreign intelligence to carry out activities on their behalf unless they have a warrant approved by a Secretary of State and Judicial Commissioner.
:: Clarifies the position on encryption, making it clear companies can only be asked to remove encryption that they have applied and only when it is "practicable".