is that the polite way of saying " first thing go to homebase, buy some plaster board and hide the problem you made"
as thats my plan B ,,,,,, was plan C BUT i had to rule out plan A when i realised that the fireplace wasnt empty behind like i thought
also the way i look at it is,,,,,,,,,, if the first floor caves in just remember that high ceilings are a selling point in london