A yellowish and acrid fog lingered over London for about four days in December 1952, blinding the city to the point of halting buses and ambulances in the streets. This event, known as the Great Smog of London, was not a typical weather phenomenon but a severe air pollution crisis. A period of unusually cold weather, combined with an anticyclone—a high-pressure system that suppresses wind—and windless conditions, trapped atmospheric pollutants above the city. These pollutants were primarily from coal, which was widely used for heating in homes and industries. The coal burned during this time was of lower quality, known as "nutty slack," which produced more smoke than the usual anthracite coal. On December 5, an anticyclone settled over London, trapping a layer of cold air near the ground under a warmer layer of air, like a lid. This prevented the smoke from escaping into the sky. Initially, the fog was not particularly dense, but as night fell, it thickened dramatically, reducing visibility to just a few meters. The sun, which was too low on the horizon for the season, could not penetrate the thick smog. Over the next few nights, the fog worsened, casting the city in a yellowish darkness for four consecutive days. Streets became eerily quiet, with cars abandoned and public transport disrupted. The smog seeped into homes and even affected livestock, with reports of animals suffocating in areas like Smithfield. The human toll of the smog was severe, though initially underestimated. Official sources at the time estimated 4,000 excess deaths, a number that already seemed staggering. However, more recent research suggests the death toll could have been as high as 12,000. This discrepancy highlighted the government's initial reluctance to acknowledge the crisis. Some members of Parliament, like Norman Dodds, a Labour MP, pushed relentlessly for action, even as government officials privately expressed concerns. Harold Macmillan, then Minister of Housing, described the smog as "really serious" in private but publicly downplayed its urgency. This internal conflict reflected the slow response of the British political system to the health evidence. Public pressure eventually led to legislative action. While Parliament debated for years, some local authorities took early steps. In 1954, the City of London Corporation banned smoke in the Square Mile, a symbolic move two years before Parliament acted. A commission was established to investigate the pollution, and its findings played a key role in shaping public policy. The Clean Air Act of 1956 was finally adopted after sustained pressure from MPs, the press, and public opinion. This event marked a turning point in air quality regulation and demonstrated the power of persistent advocacy in driving political change.