The chap from Potton has pointed out that current regulations mean that if you have 3 floors you have to enclose the stairway so that there is a “30-minute fire resistant partition with fire doors to enclose and extend the escape route to a final exit”.

There is the alternative that:

You can provide sprinkler protection to the open-plan area in accordance with BS9251: 2005, in conjunction with a fire resisting partition and door (FD20 / E20) positioned to separate the ground floor from the upper storeys. This door should be so arranged to allow the occupants of the loft room(s) to access an escape window at first floor level in event of a fire in the open-plan area. Cooking facilities must however in all cases be separated from the open-plan area with 30 minute fire – resisting construction.

BUT, it is a safety concept. A ground floor fire could push smoke up through the house. So an enclosed stairway is a safety feature.  How about a door at the top of the stairs, so that it is open plan onto the stairs at the ground floor?