Hi, i have a similar issue... a recent FRA recommended a Fire Alarm be installed in our Block - 4 Storey Conversion / 6 Flats. No idea when it was converted, no secondary means of escape, just a single stairwell. All Flat Front doors open directly onto the stairwell, doors are also mismatched, so no idea who, if anyone has a Fire Door.
The system they have recommended is...
Grade A, LD2 coverage in the common areas and a heat detector in each flat in the room/lobby opening onto the escape route (interlinked)
Grade D, LD3 coverage in each flat (non-interlinked smoke alarm in the room/lobby opening onto the escape route) to protect the sleeping occupants of the flat.
Any advice would be appreciated. Thanks.