Piccadilly Circus
The phrase "it's like Piccadilly Circus" is commonly used in the UK to refer to a place or situation which is extremely busy with people. It has been said that a person who stays long enough at Piccadilly Circus will eventually bump into everyone they know. Probably because of this connection, during World War II, "Piccadilly Circus" was the code name given to the Allies' D-Day invasion fleet's assembly location in the English Channel.