I’m studying abroad and I have seen a few of these odd structures in London. They are circular in base, bigger than the Duke library, and about 6 stories tall, though they vary. They are made only of steel supports, but do not seem to be involved in any construction. They don’t hold anything up either. What are they there for? Do people in London just like to remember using erector sets as children? Cheers.
Do they look old? These sound like tanks for the storage of gas. In particular, I think they’re associated with the storage of coal gas (derived from coal). There was steel scaffolding around the cylindrical tank. It could be that the tank part in the middle has been removed, leaving only the scaffolding. Some of the really old ones used a brick curtain around the outside rather than steel scaffolding. You can google words like “gas storage tanks” and “industrial archaeology” and look for images.