If your on low income/means tested benifits and have no way of funding the AP yourself, your likely to get a grant.
You will be required to fill an application form, that also ask about your needs and the dimensions of any equipment such as a wheelchair and the process can take up to 12 weeks at least. Your grants manager will look at your case and list what he/she thinks is suitable, although its possible to choose your own vehicle from the vehicle catagory you are awaded (Catagory C is a mid-large SUV). If you are awarded a grant, you can top this up to a maximum of 50% from your own funds, i.e if your awarder £1500, you can add an additional £750 yourself or you can choose a vehicle with a lower AP than your grant award offers. Thats the basic’s of it anyway 🙂
https://www.motability.co.uk/get-support/faqs/apply-for-financial-help/