What was the damage to your vehicle?
I ask, because if there is no damage, then no crash is deemed to have occurred, and the fact that the other driver continued without stopping suggests he/she may not have known that they had hit you..
As far as fault is concerned? That is subjective based on your description of the crash as it could potentially be deemed as split liability 3 ways (all 3 of you sharing responsibility) for the reasons you have already covered in your own account.
You would need to look and see if CCTV cameras were in operation at that location and then make an application pretty quickly as usually footage is only kept for a short period of time, but even then local authorities will only release footage to an authorised body such as Police, solicitors and maybe insurance companies, and even then at a price.
If there is damage, and it would have been obvious to the third party that he/she had collided with you, then they will have committed the additional offence of failing to stop and report a crash (unless they report it to the Police within 24 hours) and that would certainly work in your favour, but potentially, all 3 of you could be prosecuted for careless driving which (In particular driving without due care and attention which is one of the 2 sub sections) if Police were to get involved (which they won't as they are not interested in damage only RTC's,)
So, if the damage is substantial and you need to get your insurance company involved, and providing you have the registration number of the vehicle that failed to stop, all you can really do is leave it to them to sort out.
If there is no third party details, then you can still make a claim via the MiB under the untraced track, but there is an excess of £350 on the first part of any damage only claim and there are strict protocols that have to be observed.
Sorry I cannot be more positive.
