White powdery substance on houseplant

Possibly mealy bug. Try painting some of it with meths . If that dissolves it that's what it is and you just need to carry on and do the lot. If that clears it you may find it a good idea to tip the plant out of the pot to look at the roots, as sometimes they are affected as well. The treatment is the same, though not as easy because of the compost, which you'll have to wash off first. I think there is a chemical control for the roots but have never used it.

Thank you for your response. I will try the meths.

Try a 50% solution of isopropyl alcohol. That will the dissolve the wax coating that you see with which the mealy bugs protect themselves with. Also, if you have it in the UK you can try an insecticidal soap. See if that works first before you pull the plant out of the pot. Check any other plants you may have in you're home and always carefully check any new plant very carefully before you bring it into you're home.

Its called surgical spirit in the UK. same effect on mealy bug as meths, which you are more likely to have in your garage..