“People often refer to Big Ben when they’re talking about the clock tower attached to the Palace of Westminster.
Big Ben is the name of the largest bell, and even that’s a nickname and not an official one. The tower is named the Elizabeth Tower (formerly the Clock Tower), a name it was officially given in 2012 to celebrate Queen Elizabeth II’s diamond jubilee.
The clock is simply known as the Great Clock.”
– Laura Reynolds, The Londonist