No idea on make, sorry. I'd imagine tho that this should either have a diffuser or Louvre on it.

Yes, this one would likely have had a louvre, as I've seen many fixtures identical to this that had louvres on them, but it appears that this one went missing at some point during relamping?

Fluorescent lights in educational institutions often seem to end up with their diffusers missing. There were whole rooms like that at my secondary school that was built in the early 1970s. SRS 6ft Thorn pop packs with the prismatic diffusers removed and diffuser kit still present. I think it was a lazy caretaker, chalk was still very much in use in the 80s and the light output would drop due to chalk dust in the diffusers so rather than clean them, he would just remove them.