Bryan

Is 24in wide 24 ft. long [inside the ridge of my roof } of aluminium foil
tacked to the rafters not better as a top capacity than 100ft of top-wire
down the garden ?.

Don't even think about it if you are considering transmitting. The voltages
at the top end of a loading coil at LF are very high, even at modest power
levels. Several of us have experienced fires or arcing with LF antennas for
one reason or another. A loft is a bad place to have a conflagration.
A loft or attic loading coil system feeding an external antenna can work
fine provided it is well engineered, see the I5TGC antenna system in the LF
Handbook.

Either way I am stuck with 24' vertical  but my
top-loading coil and feed point and capacity can be inside the attic.

I thought that at LF,  losses through brickwork were so slight that it
wouldn't matter that the vertical was almost touching brickwork at endwall
of house

For dry brickwork that is probably true

As a separate  matter does anyone know a site that gives figures for
attenuation of sigs from an attic antenna at various frequencies ?? HF/VHF

At HF most lofts are fine. I did live in one old house where the slated roof
caused considerable attenuation but I don't know where these slates came
from. Modern tiles all seem OK.

Regards,
Peter, G3LDO