You'd think the police would have powers to do this???

[JoeRock]

Re the investigation to the rtc was anybody injured !!.
He's rear ended you so he's liable full stop and technically driving without due care.
The general thought will be it's his fault he's loosing no claims and if no injuries it's not in the public interest to pursue a prosecution.
If the accident was investigated phone records could be obtained but you would need a good time line to compare to

That rule about rear ending someone and being fully liable has actually been changed now - it's all about the circumstance, although in this one he does sound liable. Was due to a woman randomly braking hard in front of a biker at 70mph, usually the biker would have been at fault, but the court decided he braked and swerved as hard as could be reasonably expected, and applied full blame to the car in front.