Hi Tim, John - thanks for your comments.

I ended up doing a second coat with a small roller as you suggested,
and having 'conditioned' the paint with this (pricy) Floetrol stuff.
I'm not terribly experienced with painting using a roller... anyway,
the second coat has improved matters somewhat, and it's 'good enough'
now.

I think the surface is very noticable on these walls (they are the
sides of a hall) as the afternoon sun shines straight down it. This
together with the type of paint (almost thixotropic, as mentioned) and
the silk finish, have combined to make it so visible. Anyway, it'll
suffice...

Thanks again
J^n