It's not about the inability to make a decision. It's about (in the above example's) proving which party is to blame. If there's no proof either way, the only 'fair' decision to make is a 50/50 split.
Yes both premiums will be affected, a little more cash in the Insurers pocket at renewal...
Difficult scenario.
Without witnesses, the insurers would likely split liability 50/50 depending on version of events/interview etc.
It's down to proof.
Car at the back (in your scenario), Insurer: "prove to me that the vehicle in front rolled back", Policy Holder: "I can't, he just rolled...
You are correct as in the Highway code it states the handbrake should be used (note, not MUST be used) if you are to remain stationary for some time.
However, the degree of negligence by the vehicle behind (or in the OP's case, the third vehicle) who shunted you is far greater and they will be...
Sorry, but that's all wrong.
You need to look at negligence.
The only vehicle/party negligent is the third vehicle.
All claims would be directed to the third vehicles insurers.
It's really not dodgy ground. I see this every single day with the very same outcome each time.
Really don't mean...
Did your friend get the details of the car at the back of the shunt?
Did your friend take any pictures of the incident and/or cars involved at the time?
If so, inform your Insurers and pass on the details.
DO NOT give any cash to the lady/car in front as by doing so, you're (in a sense)...