Loft Condensation

Hi. I’ve found some really useful info on this site and whilst I’m typing this in London, I’d appreciate some advice. I have an attic space which has been properly converted into room space. It is boarded and carpeted. The roof was replaced with some lightweight tiles. We get occasional leaking through one electrical point in the ceiling below. Initially I assumed the cause was the shared gulley but we still have the problem after this was renewed.

The leak does not occur in heavy rain.
The leak does occur in very light snow or drizzle when freezing outside.

The loft space whilst unheated does contain the central heating tank and several uninsulated pipes. Ice damming could be a cause but hey, this is London not Newfoundland. Could it be condensation? And if so how would I remedy this? Many thanks.