...would like some tips on determining its "weight bearing" status.

I know that this is probably the kind of question that if you have to ask
it, you probably shouldn't be doing it, but, I want to knock a wall down.
;-)

The flat in question is a ground floor flat in a 100 yr old three (well,
two and a half) storey terrace. Very conventional layout. Two front rooms
separated by a hall. Three back rooms, separated from the front rooms by a
solid wall, no doubt supporting the ceiling joists which run from front to
back.

I have no plans to meddle with this. ;-)

One of the back rooms is the kitchen/dining room which would be rectangular
except for an internal "porch" area that takes a square bite out of the
corner of the room. As there is now an external porch over the back door
it would be nice to reclaim this floor space for the kitchen. The walls of
the porch are lath and plaster construction.

Would I be right in thinking that this structure is most unlikely to have
any weight bearing purpose and how could I make certain that this is the
case?

Would looking under the floor to see if there are any founds under any part
of it be conclusive enough?

Do I need to speak to building control or anyone else first? The property
is in Scotland.

TIA.

Tim