And here is my quandary: - is there any straightforward way of telling
how the ceiling is constructed? (I couldn't find anything in Google).

Ideally lift a floorboard upstairs and look though - you'll see the laths.
OR remove a light fitting - normally the holes where the cables come through
are big enough to see how the ceiling is constructed. Alternatively, if you
gently drive a 2" nail into the ceiling in a few different places you'll
soon know when you've hit a lath - it'll feel springy and the nail almost
certainly won't go through it (unless you happen to be right next to a
joist). Don't drive the nail any further than 1/2" or so, to avoid pipes
etc. above.

Andy