I'm in the process of replacing my fireplace with something a bit more modern. Having taken the old gas fire out (which was done by the gas board incidentally), I'm wondering if I can remove the old chimney breast, remove the firebox surround and then close off the cavity flue.

Having exposed the firebox, it is solid concrete with TX11 stamped on the back. It appears to be two pieces, a top and bottom. Neither of my neighbours has this, but neither were living next door when theirs was removed. So I don't know if this was a major or minor exercise. It looks like it is a drop-in unit, but I'm concerned whether it's chased back into the wall.

Has anyone seen this type of firebox before? Are these normally recessed back into the wall?, is there some way I can tell?

Any help appreciated.