Through the 19th and in the early half of the 20th century, Londoners used coal for heating their homes, which produced large amounts of smoke. In combination with climatic conditions this often caused a characteristic smog, and London became known for its typical "London Fog", also known as "Pea Soupers". London was sometimes referred to as "The Smoke" because of this. In 1952 this culminated in the disastrous Great Smog of 1952 which lasted for five days and killed over 4,000 people. In response to this, the Clean Air Act 1956 was passed, mandating the creating of "smokeless zones" where the use of "smokeless" fuels was required (this was at a time when most households still used open fires); the Act was effective, though the nickname is still used sarcastically. Many cities have since aquired the nickname "The Smoke", but London was the first, hence "The Old Smoke".
London - "The Old Smoke"
by Kristian fra Kristiansand August 11, 2010