Concerned with what exactly?

When the original 'building' was altered wouldn't there not
have been Local Authority approval papers? would these
have not been passed to present owners?

Have you had an inspection to determine quality of the renovation?

I am assuming from several of the words (e.g.chimney breast and Local Authority) that you used in your post that you are not un the US.

Most of the posters here are in the US, so we may not be able to be as heplful to you as we'd like.

If fireplaces (and associated hearths and mantles, what you would call chimney breasts) were removed, I think that would be fine in a wood-framed house where this masonry was not structural.

There is mixed need here in the US for permits for that kind of work. It's entirely a local issue, so there may or may not have been demo permits issued. If a permit was required, then it's possible there was some inspection afterward, but not always.

You could ask your Local Authority, or you could hire a structural engineer to evaluate the stability of the building. For me that decision would rest on type of building (wood frame vs stone or brick) and also what I could see of the plaster (diagonal cracks indicating settling in the area of the former chimney breasts, for instance.)

One thing that is true everywhere: older buildings always have some issues, but even those buildings with issues are generally very sturdy. That's because they are demonstrably survivors, their comtemporaries which were sketchily built have already succumbed.

Good luck to you - and we'd love to see pics, if you care to share.

L.