Interesting photos of London from 1952. This is Nelson's Column:
The photo above is from wikipedia. The smog was caused as a result of burning coal. Read the full article here. This article from the met office has further information.
This photo is from an encyclopaedia (I can't recognise the area, but the sign on one of the buildings to the right says Sheraton I think).
Apparently smog killed between 4000-12,000 people that year, when smog was particularly bad for five days in December.
Afterwards, the Clean Air Act of 1956 resulted in dramatic improvements within just years. Smokeless fuel was mandated in certain areas. This resulted in far lower industrial coal burning, and railway output was eventually diminished to nil.