The deciding factor in this question is 'while driving'. The owner is responsible for making sure the vehicle is not used if it is not roadworthy, but if they are not driving the car themselves, it is difficult to vouch for the car's condition while driving. Whoever is driving the car on behalf of the owner then becomes responsible.

According to the Road Traffic Act § 23, before driving, the driver must ensure the vehicle is in a proper and prescribed condition and that it is loaded safely according to regulations.