We occupy (lease) a small ground floor office which is part of a block containing 4 flats. The building consists of ground & 1st floor. We have our own entrance which is separate from the communal entrance to the flats. We are being asked by the local FRS to provide a Fire Risk Assessment. The landlord leasing us the office space doesn't appear to have one. I dont know who the freeholder is for the entire building. Conducting an FRA for our small office space (4 people) would be quite straightforward but I dont want to be drawn into the more intricate issue of the adequacy of fire separation between our office space & the flats above. Who is responsible for this ? The landlord ? The freeholder ? Should they already have an FRA for the building as a whole which we can refer to when compiling our FRA ?

Yes the common areas and structure of the flats must have an FRA by the Responsible Person (freeholder or commonholder) usually arranged via their agent. You still are responsible for your demise and need to consider other relevant persons in the building (the flats) but you should have access to the flat's FRA to help with that.

Thought as much. The problem at the moment is getting sight of the FRA that should have been completed for the building as a whole, particularly regarding the fire separation from our occupancy to the 3 residential dwellings sharing the building & vice versa. Quite happy to do an FRA for our undertaking but not to take on the  responsibility for vouching the integrity of the buildings fire separation.