That is completely true about the national trust. There could be all sorts of subterfuge going on there. The worry is that nobody has ever investigated it. Of course you do get those stickers, but nobody says YOU HAVE TO put them on your car. Atleast as a freemason you know who the other members are, but when I was in the NT it was so secretive that I was never sure about the others. Maybe I should have paid a bit more attention in the tea shops.
I think some members of the royal family may also be associated with the National Trust. I'm sure it goes all the way up.