Sorry forgot to mention. I think it's up to the insured to make sure it's actually done though. I' m certian if you got stopped with no mot it would be your fault.
As the driver it is your responsability to make sure that the vehicle you intend to use has a valid MOT , Tax & Insurance relevant to their intended use. Or you run the risk of getting on the wrong side of the law. As it is the driver not the owner that would be prosecuted & liecence put at risk. If the registered keeper wont pay for the MOT then stop using the vehicle or pay for it yourself.
Have to agree with gasman here.
It is entirely down to the driver of the vehicle to be sure that it's fit to be on the road.
The actual owner should be responsible for the work involved in keeping it legal but it's the driver who would be breaking any laws.
Just think of the number of truck and bus companies and all the drivers they employ, but ultimately the responsibility rests with whoever is holding the steering wheel.