Right...so had my goto guy out over the weekend to first come and sort out my generator and then to discuss the problem of what to do with this fireplace. After some tapping and drilling we have determined the following:
View attachment 1050531
The column going up is solid concrete with no central cavity.
This lovely block of pain is resting on two steel beams snuggly fit into bricks and some lintels which make up the rest of the structure.
Behind the steel though there is a cavity into which the existing fireplace extends up.
At the arrow, there is enough space next to the column and between the two beams to be able to open up a circle of about 25cm in diameter.
Squigly line would effectively be a flex tube in the cavity from a new fireplace to said hole.
With that in mind the idea has now expanded to basically redoing the entire thing as such:
View attachment 1050535
Structure to be expanded a bit to add the triangular shape on top to where the column meets the first ceiling.
Existing gas fireplace to be removed and replaced with either a double-sided wood burner or to close up the back and put a cast iron slow combustion stove in (Still in two about this, views appreciated.)
Flex tube from the top of the fireplace to the arrow to a new flue that gets concealed in the red area after which it runs exposed up the wall to go out the roof.
Entire fireplaces plaster to be stripped off and replaced with a red brick cladding which will also go behind the flue all the way to the ceiling.
Or something like that, still working on the idea.