It was assumed to be asphalt over old quarry tiles thus making excavation easier. Turns out that front living room floor had been renewed previously with a very robust(!) concrete floor. This will require additional time and labour to reduce to the required levels.
As if this wasn't enough, further excavation reveals the rear external wall, between existing dining room and kitchen, has no footing. It is literally being supported by the earth below. This will need sorting!
Also, decided to remove old chimney breast in bath room in order to have a clear wall for the stud system. In doing so discovered gable end wall to bathroom has loose brick work above the window that will be blocked off.