The critical issue here is whether or not the ability to buy your car at the end of the lease was specifically written into the lease agreement or not (from memory, I don’t believe that it was).
I recently took on Motability over their refusal to allow us to extend our lease as we didn’t meet the new criteria. I cited the fact that the option to do so was written in to the lease agreement that we had signed (by entering the PIN) and that cannot be changed mid-term without us being informed in advance of the proposed change and having the right to terminate the lease at that time due to the conditions of the agreement having been varied. Needless to say they backed down immediately and allowed us to extend to 5 years (in the end we didn’t need an extension, but that’s irrelevant 😂).
As for the ability to buy the car at the lease end, if it wasn’t specifically written in to the lease agreement then my view would be that it was discretionary and not contractual. If that’s the case then Motability would be able to remove that facility without consent or consultation. Whilst I have sympathy for those who got a car with a high AP and / or loaded their cars with options with a view to buying it after the lease had ended, if this wasn’t a contractual right then I don’t think people have a leg to stand on. There’s no harm in trying, and they may well agree to the purchase to keep the peace, but I tend to agree with others that Motability have always asked far too much for cars sold without warranty and you can almost always do far better buy buying privately.