In December 1952, a thick smog, known locally as a pea-souper, engulfed London. Although no stranger to fogs and mists, the city is built on marshy land, the pea-souper of 1952 was to prove so devastating that is caused a change in the law.
On the 5th December a combination of cold and wet weather settled over London. An anticyclone settled over the windless city causing a temperature inversion trapping the cold wet air under a lid of warm air creating a fog that lay heavily on the city. At that time most of the houses in the city were heated by coal fires and the city contained several coal-fired power stations. After the second world war the British economy was faltering and as a result high quality and less polluting coal was exported while the domestic market used low-grade, sulphurous varieties that were full of pollutants. The pollutants from domestic fires and the power stations combined to form the smog. Particles of tarry soot created a yellow-black colour which coated everything in its path.

The pea-souper was so dense that it reduced visibility causing transport to be reduced to walking speed causing major disruption to the city. Travel became almost impossible in some areas. All public transport was cancelled except the London underground. Attempts were made to keep the railways working by the use of ‘ detonators’. A large percussion cap placed on the track and activated by the wheels of trains, they were placed by certain signals to provide an audible warning to match the visual indication provided by the signal for the driver. However, they did little to reassure drivers who were working almost ‘blind’ and railway transport was cut to the bare essential of freight transport. Even walking was dangerous as the streetlamps were unable to penetrate the gloom. The smog penetrated buildings with factories, businesses, cinemas, shops and homes all affected. Many schools and some hospitals closed, except for the most urgent cases. There was a sharp increase in crime in some areas. Aided by the low levels of visibility, street robbery and housebreaking flourished.
Those with respiratory complaints were worst affected and in excess of 6,000 Londoners in total died with a further 100,000 becoming seriously ill. The following winters saw increased deaths from respiratory disorders thought to be the long term effects of the smog.
On the evening of the 9th December the weather finally changed and the smog dispersed on the wind. The death toll had shocked many in Westminster and legislation was quickly enacted. The City of London (Various Powers) Act 1954 and the Clean Air Acts of 1956 , led to a reduction in air pollution and families were encouraged to replace their coal fires with alternative. In addition, the use of cheaper polluting coal in the coal-fired power stations was increasingly replaced by the better quality coal. This improved matter greater and when a further pea-souper hit London in 1962 the death toll was only around 90.