get a RH sensor for http://www.amazon.co.uk/TFA-humidity-meter-20-99-rH/dp/B002UA9RG6/ref=pd_sim_sbs_kh_1 (circa 20quid). watch it when goes over 80% as thats the 'condensation zone' (relative to heating etc of course),but that'll allow you to see if its the lack of adequate fan/ventilation
you mention 'the edge of the attic' -
>cold surfaces which you yourself admit you have, so try to solve this.
>to much moisture which you can check with RH sensor - just because you have a fan, doesn't mean its any good.
> some of the attic insulation you pushed in to the eaves is touch the sarking felt making it wet and that in turn is wetting the plaster board helping your mould to grow.
try to improve your insulation and keep the internal surface temperatures close to the room temp. then look at ventilation, I'm a 'fan'(excuse the pun) of extract fans that have an inbuilt RH monitor so they open when required and stay closed otherwise.
best of luck and i hope this helps. paint will help but if the above are addressed you are more likely to have a permanent solution