Hi, I'm Steve, a London tour guide and owner of A London Miscellany Tours, a guided walking tour company who specialise in small number tours of the greatest city in the world!
Well in a way they are as in the case of the picture, but they are there to denote the boundaries of the City of London as apposed to the city of Westminster.
There aren’t that many that sit across roadways like those in the picture, but I think that the big ones must be removeable, but in general the ones that sit on the pavement are permanent. The thinner ones tend to mark parish boundaries.
A LONDON MISCELLANY 
I thought they were bollards.
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Well in a way they are as in the case of the picture, but they are there to denote the boundaries of the City of London as apposed to the city of Westminster.
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Such lovely markers…They look rather permanent – can they be moved I wonder?
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There aren’t that many that sit across roadways like those in the picture, but I think that the big ones must be removeable, but in general the ones that sit on the pavement are permanent. The thinner ones tend to mark parish boundaries.
LikeLiked by 1 person