What are you hoping to achieve?
The MOT is something that the police can act upon if they choose but it only carries a fine.
It is of no consequence from the insurance point of view. In fact, actually it is disadvantageous to you because they could argue they are not liable if he had no MOT and then you would have no solvent defendant to sue.
Your own insurance company should be dealing with this anyway.
Can I clarify anything for you?Jo