Insurance and mechanical failure

[Snowboy]

This is just a theoretical question based on the bodge thread.

What would happen if a car had a mechanical failure that caused an accident?

Let's assume fully comp insurance.
Say a brake calliper stuck causing a swerve and a crash.
£5k same to your car £5k damage to someone else.
Would both cars get paid for?

Would the person who last touched the calliper (or hadn't maintained it) be liable at all?
What if it was bodged rather than fitted properly?
Would the insurers even pursue that line of questioning?

Is there anything else relevant?