Is it something that has just developed? Is it on all leaves or just a few?
It could be a fungal infection - in which case spray with a solution of baking soda (1 teaspoon in a pint of water with a bit of soap). Makes sure to spray undersides of the leaves as well. You'll need to do it every few days - it isn't an instant solution

Alternatively you have quite an attractive spotted aspidistra or someone's been painting the ceiling :o)

Ha ha thanks - its something thats developed and isn't on all of the leaves. It looks to me like mould so i think you're right, i'll try your treatment. Do you know what might have caused it?

If those spots are clumps of sticky fuzz, it might be mealybugs.

Fungal infections are generally connected with warm, damp conditions, not enough air circulating, and such like. Spores could come in from anywhere.

They do look a bit fuzzy...

Just looked up mealybugs, dont think its them