One way it is possible to target the Scheme is to change their VAT exemption so only modified vehicles are eligible whilst the majority of cars, which are standard, would be reduced only by the negotiated discount. I’m not sure that’s worth billions though.
I can see that happening with major modification as per VAT guideline, the knock on effect non VAT except vehicles servicing and possibly insurance will attract VAT, with the increased AP it will become unaffordable for most disabled customers.
Unfortunately I have suffered a brain injury and occasionally I get confused and often say the wrong thing.