I do, Tony, I do.
Here's an idea.
Produce a laminated information card you can attach to one of these things (only needs one hole punched in it, or 3 if you're being really lar de dar). On it, print summat like:
"You probably think you are helping improve safety by putting this bit of plastic into your socket, but the opposite is true. Whilst your good intentions are clear, you are making matters worse. UK 13A sockets are inherently safe...."
... then words of your choice pointing out the whys and wherefors, and a link to the fatally flawed website.
Bung a "danger of death by electricity" yellow triangle on it too.
This will be really useful when you see them out and about (libraries, pubs/function rooms etc) and the people there to complain to couldn't give a monkey's because it's not their job and/or they don't want to get fired for removing what their boss might well insist is a "safety" item.
I propose that this gorilla awareness campaign (~waves at GMES~) might have some effect.
Customers will notice it and ask questions. They might well have them at home and get rid of them (double win!).
The owners (or their staff) will notice it. If you word it right, so they don't feel too foolish ("We know your intentions were honorable" or whatever) then they might do summat about it. After all, if they have to remove the piece of plastic to remove the notice (to bin the notice), they are more likely to bin the bit of plastic too, rather than go to the effort of putting it back in.
If you need some money to make the laminates, I'm happy to bung you a few quid.