Free vehicle tax with enhanced mobility part of PIP

Hi first time posting, so may make mistakes.

My partner has just been awarded the enhanced rate of PIP for daily living and mobility. He has been sent a certificate which he can use to claim free car tax. He isn't able to drive and so I use my car to take him to hospital appts, get shopping, scripts etc for him as I am his full time carer.

On the DVLA website it says that someone can apply for free vehicle tax IF the registered keeper "USES THEIR CAR ONLY FOR THE DISABLED PERSON... TO HELP THEM, FOR EG, TO GET PRESCRIPTIONS OR GO SHOPPING FOR THEM." I get the point but it makes no sense to me: are we thus supposed to run two cars in case I were to ever need to use the car for my own purposes such as a hospital appointment etc? Surely no-one can afford to do this, it seems crazy. We have a Blue Badge for parking which I obviously only use when I have him with me as I don't need it but the idea that I can't use a car for anything else is bonkers. I am not working as I am his full time carer but might occasionally want to use the car for something not connected to him.

I would be very grateful for others input/ advice about this. Thanks.