Thanks for the reply.
I feel like I have little choice but to rip it out and start again, what really hurts is the room was basically finished bar flooring and skirting.
Now I know how badly it was done and how loose the rubble is beneath the screed I don't want to hide the problem under £1000...
We have a room in our house that was converted from a garage approx 40 years ago. There is now a concerning crack that runs parallel to the external wall (150mm away) across the face of a bay window (put into what was the side of the garage originally). The floor then slopes slightly away from...