Purpose built Hostel type premise. Good level of compartmentation. 
Presumably built initially for a stay put with one S/D and one heat in kitchen Grade D non interlinked. 
However the communal area part one system has been linked to the small flats with one detector in the hall. The sounders are external though in the communal areas. 
is the level of flat detection still commensurate with the current full evacuation? Presumably the sounder decibel level would have to be audible but what about the two non interlinked grade Ds? Link them to the part one or is one detector in the hall way enough? 

Sounds more like designed for sheltered accommodation. These operate audible full evacuation in common areas with stay put in flats (so common system shouldn't be heard). Flats then have a local Grade D system in each just for protection of the flat occupier (which in sheltered would be linked to telecare)

Whilst the common system doesn't need to go in the flats at all it's not uncommon for the common system to have a detector (no sounder) in each flat hall ways as a back up in case a flat catches fire  whilst the tenant is out or they don't respond.

If it should be a complete full evacuate block including the flats then the only main difference would be the common detector in the flat hallway should also have a sounder - no need to try and link the Part D systems

Great reply as always. Thanks