[Photos] Opening up a dodgy fireplace advise

Our chimney breast was to be getting damp, so we took the plaster off to inspect what was going off behind. The brick work is a sorry job, and the hole pictured was crammed with loft insulation / newspaper.

I want to open the fireplace up and allow it to breathe . The problem is there doesn't seem to be a lintel, so I wont be taking any bricks out.

How would you proceed?

https://www.dropbox.com/sh/lij7rf5b059jhpp/AAArSYuhoUOHd-TBtI_LQCooa?dl=0

Many thanks,
BST

It looks as though the original construction was stone block with the lower bit patched up with bricks. From photo2, there would appear to be a lintel about 9" higher then the big square block (then thin black lintel, then the main one, or even one higher?). In old properties like mine, you get a Georgian opening at 4'6" (huge stone lintel), then a Victorian thin steel bar and brick arch a bit lower, then A 1970s concrete one at about 30".
Frank