Originally Posted by: ThePatheticBaker 
It is not a product name known here in (the original) London. I have lived and worked in/around London for 40+ years and never once heard of "London broil".
It was all the "rage" in the 60's in the US. Mostly as a BBQ cut, cooked on an open grill. I remember when London broil was an expensive cut of meat. As such our family bought chuck roast, which was much cheaper. Now the tables have turned and chuck roast is pricier than London broil.
It's a flat cut roast basically. 2-3" thick and very lean. Weighing in at 2 pounds or so.
I like Fyretigger's idea of flash-freezing, slicing thin, and marinating for an extended period of time. It's how I would cook Santa Maria style tri-tip, albiet the tri-tip is a bit thicker cut, perhaps a 3/4" or so.