I second the above.
You have to respond as you where the recorded car keeper.
It doesnt matter that motability are the owner of the car as the legal responsibility of the keeper.
If you fail to respond to the NIP (notice of intended prosecution) you are taken to court for the offence of fail to notify of driver (MS90) which is points and a fine but the important bit is some insurers treat this offence as serious as drink driving and refuse insurance.