Whats this in my fireplace?

[Damon]

Hi everyone,

I found a hollow void inside the brickwork of my fireplace recently. Originally I assumed it was am old bread oven but as I can't find where the oven door would have been I'm now not too sure. The void has an opening at the top with a surrounding metal collar and then a channel above that runs around and into the main chimney itself.

What do people think this originally was?

I've attached a few images below.

Many thanks.
Damon

 

[Damon]

 

[Damon]

Any thoughts?

 

[Andys]

A smoker for an individual kipper?

Some sort of flue access?

I'm not really helping am I :|

 

[worms]

Is the (?rubble construction) wall to the left of the same age? It is difficult to see from the pics but it looks like it cuts across other marks on the brick wall and the fireplace looks closer in to the wall than might be more usual? Just wondering if there might previously have been more space for an oven opening. Also, could parts of the brickwork be later infill of the oven opening - much of it looks like infill, rather than original wall!