as the spouse you can only use the Motability car if it’s for the benefit of the Motability customer (so no personal use). I think that that is crazy as it can mean, as it has for us, that we need to have two cars.
As @swwchris correctly states, you do not need to worry about this. Many disabled people are unable to drive but live with a spouse who can, therefore clearly only one car is required. In this instance, you can use a Motability car in exactly the same way as you would a sole private car. We are in this situation (my wife is the recipient but cannot drive any more, so we only need one car) and I clarified this situation with Motability when that time came. I use the car for personal use regularly and it is not a problem at all. We are now retired, but even if the able bodied spouse still works, it is even permitted for the able bodied spouse to use the car for commuting to and from work. So, in summary, you do not need to be running two cars unless you want to. It’s a shame that so many people misunderstand this as there must be an awful lot of people incurring substantial and completely unnecessary additional costs. A Motability car on its own is costly enough!