A now I see !!! If you already have proper fire doors at the appropriate
points
on the stair-well, then you're OK. As long as the new part of the
staircase is
not fully open all the way down to the open plan part, then you're sorted.

The way I read them (I may be wrong) is that the stairs are the primary
escape route and your escape route should be protected all the way to one of
these two points.

a) An outside door
b) A point where there are now two independent exit paths, each of which may
be unprotected, but the fact that there are two doesn't matter.

(b) is most likely to arise if the stairs lead to a downstairs hall, but the
outside doors are elsewhere, such as a back door through the kitchen and a
front door through the lounge.

This doesn't just apply to new parts of the staircase, but the entire
staircase that is required for escape during a fire.

Christian.