Attic condensation is usually caused by warm moist air leaking from the house into a cold roof void combined with inadequate ventilation. The fix is to seal the ceiling plane and restore cross-ventilation, not to add heat.
The classic pattern is black mould on the underside of the underlay and damp insulation, worst in cold weather. It usually follows an insulation upgrade that blocked the eaves ventilation path or a bathroom fan ducted into the roof void rather than outside.
Sealing the ceiling — attic hatch, downlighters, pipe and cable penetrations — reduces the moisture reaching the void. Restoring a clear ventilation path at the eaves lets what remains escape.