Hi Tony,
The blocks are indeed as you describe.
I have spoken with others and all agree that, as one could make a case for either scenario, price per stair and make sure you cover the extra costs involved. It does make pricing easier as its a simple base price, plus a set amount per additional floor.
As regards this particular situation the client is the local authority housing provider-LA- and, they say, they receive advice from the fire service-FS-who are also part of the same LA.
I think there is a feeling that they must go along with whatever the FS advise however, when I question them along the lines you mention the responses are the vague "we have been told" and this is made worse by their inability to differentiate between what they must do and what others would like them to do.
Allan