@wingpig - provided both parties stopped at the scene and exchanged details you've complied with the requirements of a 'reportable accident'.
In your case you can retrospectively report the collision. It won't be investigated due to the described 'slight injury' (no disrespect - just Police terms) but it is recorded on systems for info.
I'd always advise to call the police at the time of the collision especially if there's the inference of an offence. You'll get a unique reference number and it will allow a decision to be taken on police attendance or not.
Personally (not official police line) I'd recommend using a specialist cycling solicitor to handle your claim. They're generally very thorough and will consider things you've not yet thought about. The minimum they will require is the registration of the offending vehicle to get the ball rolling quickly.
If you look back on Cycle Law Scotlands Facebook page they've got a post about this including a copy of the information slip the police give out which might be useful to all.