But it’s never been that way in the UK. If you were suspected of planning a murder/bombing/atrocity/etc they could bug your phone even 50 years ago. And personally I’m quite glad about that!
Back then phones were as personal as a public phone booth. The way phones are used today resembles cybernetic enhancement more than tool use. That's where the concern for privacy comes from. There's a bell curve to technology adoption and some people have hard time processing this, but things are generally moving in the direction of increasing cyberization. Government messing with privacy can have two effects: (1) halting the cyberization by ruining public trust in the technology once for all or (2) planting seeds of an unimaginably totalitarian society before most people realize where this is going.