Yes Mike - I think that you have it right.

We went up to see our Social Services Assistant today as we have had a change of car and they have now written to Tarragona to inform them of this so that the tax-free qualification can be changed over to the new vehicle.
She also got my wife to fill out another form so that she can be issued with a card as proof of disability and so be entitled to other concessions, including discounts on the purchase of a brand new car if we ever want one.

So all you persons with disabilities who are out there make sure that you contact your local Social Services Assistant in order to claim your entitlements.