Yes, the law is very clear on this and the principle is very simple: The driver of the vehicle is always responsible for it being in fit condition to be drivien on the road. There is no way, legally, that you can 'off-load' this responsibility onto another person.
Hence, if you are driving an 'unknown' vehicle - hired or borrowed from a friend - you should always quickly check the legal basics because it is you who are legally responsible for them. If somebody is driving a vehicle which is illegal in some way then it is their fault for not checking it.
You will also notice that on most vehicle hire contracts it states that you have checked the vehicle was supplied to you in fit condition when accepting it.
If the police pull you over for having a light out or something and you politely explain to them that it is a hire car they might be lenient towards you and just give you a caution and tell you to fit a new bulb before driving any further - but they can prosecute you for driving a dangerous vehice if they feel like it.
Kevin.