Back in the early '80s, when my first husband and I were living the starving grad student lifestyle, his thesis advisor used to have the lab team over every few months for a feast: London Broil. It was fabulous.
There is an art to making London Broil that involves marinating the meat, turning it frequently while broiling over a high flame, and then allowing the meat to sit five minutes before slicing it diagonally (the knife is perpendicular, but the cut is across the grain).
I've essayed London Broil a few times in recent years and have always been disappointed by the results: tough, with a liver-y taste. Reading up on the recipe today at Cook's Illustrated website (subscription only) I discovered why.
Traditionally, London Broil was made with flavorful flank steak. However, in the past few years, use of the flank steak for popular dishes like fajitas has driven up the price, and supermarkets now sell their less-expensive steak cuts (chuck, and top and bottom round steaks) marked "for London Broil."
So, if I want London Broil to taste like real London Broil, I will have to ignore the store labels and and buy flank steak. Next time. Grrrrr.