Help! Houseplant mildew attack
 

More and more of my houseplants are getting white powdery coatings on the
upper surfaces of their leaves - particularly umbrella plants. It's the
first time I have ever seen this and can only put it down to the very damp
air we have had in Scotland for the last few weeks as it's now happening to
plants which do get good ventilation. I did post earlier in the week when
the problem was limited to a room where the ventilation is not so good.

Short of putting the central heating on to dry the air out, any ideas of
what I can do? And do you think it would be enough just to wash the mildew
off the leaves and then spray with a fungicide, or do I really need to
remove all the affected leaves?

Any advice will be gratefully received before I'm left plant-less!