Riggie
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Those we see parking on double yellow lines, slapping down a blue badge certificate on the dashboard then leaping out of the car must have lied on the application form."*
The person you see might be a companion going into somewhere to collect the badge holder or returning to the car after dropping them off. This is a totally legitimate use of the badge (if you read the booklet that comes with them).
The one that gets my goat and is in fact NOT allowed is the disabled person sitting g in the car on double yellow lines or a disabled bay while their companion goes and does their errands. If the disabled person is not getting out of the car then they don't need to use the badge.
What I meant is what you describe in your last paragraph, Riggie; sitting in their cars on double yellow lines or even across people's drives whilst whilst younger family members go about their business! If anything is said (eg "could you just move so I can get in my drive) they wave their blue badge and smirk.