Rose and Mickey have lunch by a fountain in episode 1x01 "Rose". From season 7 special "The Day of the Doctor".
Source: The Doctor Who Locations Guide
Source: The Worldwide Guide to Movie Locations
People celebrate in the square after the war is won.
From episode 4x01 "The Yanks in the U.K.".
Sherlock holds up a sign in front of CCTV cameras in the square to contact Langdale Pike in episode 2x01 "Step Nine".
Diana and the team attend a victory celebration in the square and mourn the loss of Steve.
From episode 2x01 "Samaritan".
From episode 1x03 "Movers & Shakers".