A few years back they started making you show your ticket to park in official stadium lots in Buffalo. But there's also a TON of private parking around the stadium where stadium rules don't apply. It's in a quasi-residental neighborhood and people sell parking on their front lawn and back yards.
Proper tailgating doesn't exist at Wembley. There's only one parking lot within a two mile radius of the stadium, and the NFL put their own "tailgate" party (which you need a ticket to get into) and they basically put their own food/beer outlets on there and charge the same prices as in the stadium (Can't remember the prices for beer, but I know a half pint of Cola was about $4). I do feel sorry for you guys who have been able to tailgate properly in the past, but with the game becoming more commercialized it comes with the territory.