The registered keeper of a vehicle should be the person that ‘keeps’ the car on a day to day basis and would normally be the primary user. They will be the first point of contact for the police for any offences or queries relating to the use of the vehicle. They will also be the initial recipient for parking tickets, motoring offences, fines etc and are also responsible for making sure the vehicle is taxed, insured, is road-worthy and has a valid MOT.
the owner of a vehicle is not necessarilly the registered keeper responsible for tax/ins etc, the primary responsibility is that of the registered keeper. whilst motabiity own the car you are the registered keeper and as such would be the first person contacted regarding fines,speeding etc.
for most users motability claim the disabled exemption on your behalf but will allow you to move it to a higher rated privately owned vehicle as long as you pay and are responsible for taxing the motability owned vehicle.