It could be Red Lily Beetle. The black fungus is actually their poo, and covers the leaves liberally. The lavae will also cover themselves in this stuff, and will start munching on the leaves killing the plant.

They tend to only affect the southern part of the UK, but are spreading north slowly (the RHS is keeping a record, and want postcodes of affected houses).

I have about 10 pots of lilies side by side, and for the first time three have been attacked this year. I have treated with Ultimate Bug killer (really only works on the larvae), the adults (dark red in colour and tend to be on the underside of the leaves) you will have to pick off by hand. Apparantly there are no natural predators.

This topic has been discussed in this forum recently, and you can find other peoples experiences he
http://www.gardenbanter.co.uk/search...der=descending

Good Luck.