Government plans to give the police and security services new powers to monitor all emails, web visits and phone calls must undergo a "fundamental rethink", Nick Clegg has warned.
The Deputy Prime Minister said ministers needed to "go back to the drawing board" after a committee of MPs and peers found measures supposed to enable investigators to keep pace with technological developments went far further than necessary and amounted to overkill.
The committee, set up to examine the draft Communications Bill, accused the Government of using "fanciful and misleading" figures to support its case for the legislation.
Mr Clegg said ministers must take account of the committee's findings and that the Bill - dubbed a "snooper's charter" by critics - could not proceed in its current form.
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Almost a fifth of hospital patients were also unable to reach their call button, a report warned.
At least 2,400 cancer sufferers die needlessly every year because their GP does not refer them to a specialist quickly enough.
It comes after shadow chancellor John McDonnell made a surprise U-turn on the Tory budget vote which is due later today.