The criteria for VAT exemption is very strict. It only applies to brand new cars, you have to have permanent adaptations fitted prior to registration and you always had to be a wheelchair user. Criteria may have changed, as they tightened up on it as some people were buying VAT free and then selling at a profit. The info can be found on the HMRC website.
Things must have changed cause you only had to be disabled but not necessarily a wheelchair user, any adaptation counted towards getting the VAT off (even a steering ball?) but you needed to be able to justify it to HMRC. It can (could?) also be applied to a used car but only on the dealers profit margin that gets paid to the Gov. So for example if a dealer makes £1k on a car, then deducts his expenses of say £500, then you could claim the VAT back off the other £500? I bought a bike that way once 😁
Because of it being abused, you could littery buy a new car every day if you had the money… they changed it to one every 3 years?
As I said thing have changed and it’s been a few years for me but one of my friends still buys a new car every 3 years.