DVR

I am working on a renovation of a Victorian house which is split into two flats (sketch attached). There is a small entrance lobby shared by the Ground Floor (GF) and First Floor (1F) flats. Both doors to the flats are fire rated with smoke seals. The 1F flat is under 4.5m above ground level and it doesn't have a loft. The GF flat is open plan and each room has a direct escape to the outside via a window. As part of the renovation, the approved inspector is asking us to introduce an internal protected hallway in the GF flat by putting a door is the corridor. Why is this necessary if we already have a protected lobby between the two flats? I had an identical project signed off in January 2020 without the additional door. Have the regulations changed since then? Where in document B1 is this explained?