There are lots of reasons why the demand isnt lawful, the car reg being one of them
- they wont have bothered to check but even if they did they are just too greedy to give a toss, they want your money and that is all they care about.

another is that blue badge scheme doesnt apply to off street parking but the stores have to have disabled parking or they get clobbered by the council and dont get planning consent.

Now in scotland the blue disabled parking plates do mean somehting so that means a paint job isnt enough to make a disabled bay legally enforceable regardless of what the council planning people want.

the method used to send their demand is dubious as it relies on an interpretation of the law that wasnt intended and certainly the slapping of the red ticket makes it look like one method is being used so they should follow that protocol.
they dont because it delays them grabbing the money and they dont rely on keeper liability anyway so why pretend to follow the law?

for this last reason it is wise to still say nothing until 2 months have passed since the issue of the red screen damaging blurb.
now that would be an interesting challenge, as they arent issuing you with a deamnd why are they placing anything on the car and risk being sued because they cant use any of the info inside the envelope as evidence.