probably an atmospheric inversion or some other type of ordinary stilling of the winds around London. They have had a bit of wind this winter, so this calming is ‘on the unusual side’ and the London fogs are nothing like they use to be during WWII and earlier.
Just a political tempest in a Londoner’s tea pot.
Correct. There has been an unusually prolonged blocking high (displaced Azores High) over southern Britain for most of the past month, with very light winds and subsiding air. (In the South West, where I live, we're about to break the January sunshine record).
The notorious London smogs of the 19th and earl 20th centuries, referred to in the article, were caused by the burning of untreated coal in open fires, which were then the main source of domestic heating. That changed with the introduction of the Clean Air Acts of the 1950s/60s, which made treated ('smokeless') coal obligatory in the cities. Nowadays hardly anyone has open fireplaces, except for effect.