These two bollards stand at diagonally opposite corners of the crossroads between Hill Street and Chesterfield Hill in Mayfair. They are Grade II listed and have an entry as such on the Historic England website (https://historicengland.org.uk/listing/the-list/list-entry/1066632). There they are dated to the early nineteenth century and described as cast iron of the cannon type.
If you look hard you can just about see parts of what originally would have been clear, cast text half-way up the bollards, marking them as street furniture belonging to the parish/vestry (i.e. council) of St George’s Hanover Square, now much blurred by centuries’ worth of paint application. This is the local authority that covered this area at the time.
Bollards like these were intended to protect pedestrians from large vehicles that would otherwise be tempted to cut the corners. Bollards in the general sense of short sturdy posts were first used on ships and quays to aid mooring, etc. The ones on quays were often recycled cannon, partly buried muzzle-first in the masonry, with the breech end giving the rounded top. This is the origin of the design of our purpose-cast ones.
Image descriptions: two colour photographs of black-painted bollards standing in the kerb, between tarmac street in front and flagged pavement behind. One photograph shows a building behind and the other a fuller view of a street. The bollards are cylindrical, narrowing slightly upwards, have a section of a sphere as top, and have three flanges around them, two towards the top, one towards the bottom.
(Photographs courtesy of Tim Reid)