I have a school with manual call points only and for a number of years they have been advised via FRA to  upgrade to and L3 system? I have refer to CLG guidance and BB100 and the observations in the FRA.  Anything else can I persuade them to do this? To note they are very small school over two floors they use various two escape routes including through window escapes on to metal/balcony stairs  in some classrooms and they have smoke detectors they have installed themselves on escape corridors. Situated in multiple occupancy building with brick walls wood ceilings. Flats and offices as other tenants and a very old and functioning alarm panel within the  main building. A listed building as well. The issue for me is fires may go unnoticed if a classroom or room is not in use.

If it doesn't use CLASP and is just used as a school during the day then technically a Category M system suffices. Add extra curricular use, sleeping risk or the fact that it sounds like the school doesn't have it's own site and is in a multi tenant building and you are looking at anything from L3 upwards.

The flats are more of a concern as I doubt it's purpose built or compliant modern conversion and without detection there will be a significant risk (especially as residential and non residential uses shouldn't share escape routes unless there are protected lobbies)

The residential smoke alarms aren't suitable and are pointless anyway - you'd notice the fire before activation if in the room & if the room is empty they won't sound throughout the building.

I'd suspect poor fire doors and compartmentation too.

One worthy of an enforcement audit!