You did indeed send two different lots of documents, but there are massive holes in it so I don’t know the whole scenario.
You have asked two unrelated questions about the same incident. I understand that.
This would be dealt with through the MIB uninsured and/or untraced drivers scheme. Sometimes I pass liability onto the stolen vehicle insurer, sometimes it goes through their own process.
What you haven’t mentioned is the fact that he is alleged to have hit the vehicle in front first before the vehicle behind hit him.
If that’s the case, then he would normally be liable for the damage to the vehicle in front on the basis that he must have been travelling too close or too fast otherwise he would have been able to stop in time. That is what the insurance company seem to be alleging.
There is then the further incident which wasn’t his fault where someone ran into him. Classic concertina accident.
There is no suggestion, from the insurance company documentation, that the person that ran into your son pushed him into the car in front because of that was the case, I cannot see any contributory negligence.
If it were not for the fact that your son hit the car in front first, then he should be getting 100% payout.
With regard to the other issue, I don’t know what you want to achieve here. You almost certainly have a complaint to make against the solicitors that cause the problem by not paying the bill and if the complaint to the solicitors doesn’t work, then you can complain to the Solicitors Regulation Authority and the Legal Ombudsman. It would be useful to know exactly what you wanted to get out of this second problem.
I am now until later but will pick this up then and then, I will be online and off-line spasmodically at the weekend.