Sometimes, it really is true — they don’t make them like they used to, even fogs. London was once the home of the pea-souper – but have you noticed one lately? That’s almost certainly a good thing, though. The worst ever hit in December 1952: “an all encompassing smoke-laden yellow smog that killed thousands”. This kind of killing fog is, happily, no longer a feature of London life (hooray for people no longer burning coal to keep warm), but it is only one manifestation of what is an otherwise alluring meteorological condition.