Ah. That gives another clue! The vertical beam you will note has much

more substantial rafters each side than all the others. It also has a

pair of stays from those rafters to the base of the beam.
Don't know if it makes any odds, but those 'big rafters' seem to be
supporting larger beams (spanning the full width of the loft and held
in the brickwork at either side) which in turn support the main
rafters.

Could we have a photo of how those stay beams (i.e. the diaglonal
ones
that run between A abd B or B and C in my diagram above) attach to
the
rafters?
Don't have a photo of that bit (not yet anyway), but they're basically
diagonally notched in, similar to how they're attached to the king
post: http://www.pciq.co.uk/pics/kingpost.jpg
The 'notch' side is at the bottom, if that makes any sense at all.

to ceiling height (2.9m)... if that makes sense.
Floor to ceiling height on the landing for the loft ladder?
Yup.

Nope - might have been used for temporary support of timbers while
the
place was being built?

That's the only thing I can think of - very conveniently placed for a
brand new floor me thinks... :-)

Andy