your comment re "Plod have a tendency to stop them talking to you and have even been known to steal details and refuse to disclose them" is spot on - let me tell you how nottingham police treated me;
a few years ago i was waiting at the traffic lights on my new XJR1300, lights on and wearing a flouro yellow tabbard, when some guy in a Corsa went into the back of me. I was shook up but didn't drop the bike. I put it on it's stand and made a note of his reg number and went round to him (he was still sat in the car) - I was polite to him and asked him if he was ok?. He sat there and told me another car had cut him up and caused him to switch lanes and colide with me while I was stationary... I told him not to worry and insurance would sort it and told him to park in a nearby busstop and we'd sort insurance and contact details etc.
but as soon as I started to push my bike to the side of the road he just drove off as fast as he could!
another car gave me their details as a witness. I went straight to the police station and provided the reg numbers and told them what had happened, a few days later a copper from Carlton Police station called me and told me the car was registered to a local woman, they'd been to see her and her husband wasn't insured for the car. the husband had said "oh yes I saw that happen right in front of us the other night - a car exactly the same make and model as ours hit that biker and drove off - the biker must have taken our number by mistake"
no way did I take the wrong number - it was the first thing I did! The Police said it was my mistake and refused to take the case any further, and wouldn't return the reg number details I'd provided to them .So this wretched little car driving uninsured idiot managed to lie his way out of it and get off scot free!!
my advice to you all - make sure the police attend the scene and keep copies of all the details you take!
And don't trust Nottingham Police as far as you can blow them!