For example , London is a city , but people often call it `` London town '' ( `` the City of London '' is a part of London where there are a lot of banks ) . For example , Greater London is sometimes referred to colloquially as `` London town '' . ( The `` City of London '' is the historical nucleus , informally known as the `` Square Mile '' , and is administratively separate from the rest of Greater London , while the City of Westminster is also technically a city and is also a London borough ) .