Anyone who has read much English fiction from the late 19th or early 20th centuries will have come away with a powerful impression of London as a city shrouded in impenetrable, dank gloom.
'In the third week of November, in the year 1895, a dense yellow fog settled down upon London,' began Arthur Conan Doyle in his Sherlock Holmes story, The Adventure of the Bruce-Partington Plans.
The author went on to describe 'the greasy, heavy brown swirl ... condensing in oily drops upon the window panes', and how in the streets 'the figures loom up, are dimly seen, and then blend once more into the cloud-bank'.
The Secret Agent, Joseph Conrad's novel on urban terrorism, owes much of its uneasy atmosphere to recurring descriptions of the yellowish haze which engulfs and obscures London.
Again, in the opening passages of his most famous work, Heart of Darkness, Conrad writes repeatedly of 'a mournful gloom, brooding motionless over the biggest, and the greatest, town on earth'.
Seen from the Thames estuary, he describes how 'farther west on the upper reaches, the place of the monstrous town was still marked ominously on the sky, a brooding gloom'. That depiction should leave the reader in little doubt that the real 'heart of darkness' Conrad feared was to be found not up the River Congo but on the River Thames.