in Burger King in the US the burgers were the size of a small plate! Much bigger than what we have over here...
I've popped into BK in Piccadilly Circus and other spots, and I suspect that what's more commonly served over there is similar to what we in the US call the Whopper Jr., vs the american Whopper.
Went to a "New York style" deli here in Florida the other day and they prided themselves on serving "overstuffed sandwiches" -- just like what the snowbirds expect when they dine out up north. The damn things are literally 10 cm high or more.