What I know, is it depends who's on the wrong.
Scenario 1, if the 3rd party guy is on the wrong, he's sorting himself out and his insurance will pay the the comprehensive guy regardless.
If it's the comprehensive guy on the wrong, the 3rd party guy and the comprehensive guy will both get their cars fixed by the comprehensive insurers.
I could be wrong, someone in insurance, clarify...
Only a third party is entitled to compensation in case of an accident, e.g. if you were to collide into another car and both cars get damaged, your insurance will only pay compensation to the damage on the other car if you are the cause of the accident while comprehensive covers both your car and any third party