Home DIY

I honestly think that you need to get a professional to come and see check things before committing to taking out that concrete no matter how tempting it is.

Concerns I would have:

1. The property is built into a hill you say. The external wall could be acting as a retaining wall taking out the concrete could remove some support, especially if the foundations are less than optimal for example in a building of that age they could be no more than spreader corbels (or worse no foundations at all).
   
2. Are there any services under the concrete?
   
3. Even if the other two are not an issue from what you describe there could easily be other issues and there is no way of knowing this until you start the work
   
   

I know you have deadlines looming but how hard are these?

In your situation I would want to get the opinion of a structural engineer. At the end of the day by spending a few hundred quid now you will be covered by their professional indemnity insurance should things go horribly pear shaped.

From all I have seen from the situation the best case scenario is the concrete is only a bit of blinding and you can break this out dig down and sort the floor. The other scenarios could be catastrophic. Alternatively as has been put forward by @Airhead scribe the floor "flat" with hardboard.