Kick-out in wall?

So I have a terrace house that had an attic conversion when we bought it and I have always wondered why there is a big kick out in this wall. The only think I can think of would be a chimney stack and while there are chimneys (that are purely aesthetically) there are no fire places (and never have been).

Would a chimney stack need such big support? Any other ideas that might save me cutting an inspection hole?

Thanks in advance x