Gosh thank you all - I will have a think and maybe phone around for some quotes for a spec. What I'll do is report back which may be helpful to other readers :)
Hi
I have a 762mm Internal Doorway downstairs.
I want to install Double Doors to a Kitchen/Diner (1981x1372x44), and just looking for advice.
Upstairs Wall
The Wall I think is Concrete Block, though I am not sure if its hollowed out. It is 133mm with the render so I think its fairly standard...