Why would you need afd in an office building.
just to quote a few from Table A.1 of BS5839-1 which could apply to office buildings:
a) Buildings in which other fire precautions, such as means of escape, depart from recognized guidance.
b) Buildings with "inner rooms", from which escape is possible only passing through another ("access") room, where there is inadequate vision between the inner room and the access room.
c) Buildings in which automatic fire detection is required to operate other fire protection systems (e.g. magnetic door holders)
d) Situations in which fire could readily spread from an unoccupied area and prejudice means of escape from occupied areas.
e) Any building in which automatic detection is provided as a requirement of a property insurers or to attract an insurance premium discount.
I'm sure there must be other reasons which could apply.
I haven't got a clue who was involved in creating BS5839-1, but I imagine they would know what they are doing. They are my heroes and I look up to them! 
I think those would be control measures coming under a Cat L5 system.
That might be true of some of them, but even L5 has automatic fire detection. More applicably the last one might relate to a P1/P2 category system.
Anyway, the answer answers the specific question correctly.
And I'd have thought Mr C.T. would know all this.
