I have previously spoken with Motability regarding this issue and concur with that which MFillingham has stated, above. From such conversation, my understanding is, it would be deemed inappropriate use, owing to the voluntary work not being of any benefit to the person awarded the PIP and thus, the Motability Customer. May be worth contacting Motability for clarification.
Interesting, because I had a similar conversation with Motability when my wife became unable to drive and we no longer needed two cars. They had no issue at all and said what I stated in my last post.
If you think about it, there will be many thousands of married Motability customers who have just the one car, so to say that the spouse could only ever drive the car when it’s for the direct benefit of the benefit holder would render the scheme pointless for the vast majority of them. Of course, there’s also the issue of how the hell would they ever know.
I maintain that the rules are there to prevent blatant abuse of the scheme, not to curtail normal day to day activities of a couple who have one car.