If a company allows employees to use their personal cars for tasks beyond normal commuting—such as driving to another site, collecting items for the workplace, or travelling to meetings—does the employer have legal responsibilities under health and safety laws? Even though the car is privately owned, is the employer still required to check things like business-use insurance, MOT, licence validity, or carry out basic grey-fleet checks? And if the company doesn’t do this, could they still be held accountable if an accident occurred and the employee’s insurance wasn’t valid? I’d appreciate your thoughts on how much responsibility the employer actually carries in this situation.

http://forum.iosh.co.uk/posts/t134718-Employee-personal-cars-used-at-work

seems you have already answered your own post