just discovered mildew in a wardrobe. what is the best way to get rid. & what causes it? thx in advance

Sounds as though the wall behind is damp or you maybe have condensation in the room and not enough heating/ventilation. You need to try to dry the wardrobe out thoroughly - a warm room with the doors open for a few weeks possibly. If you think the wall is the problem, move the wardrobe somewhere else.There are mildew removers on the market but I don't know how affective they are.

thanks, I have washed out with 4.1 dilution of bleach. the wardrobe is a built in one. the bedroom door is always open and has good ventilation, so not sure what has caused this. I will leave the now empty wardrobe door open and give good ventilation. I may have to lift the floor of the wardrobe and clean away mildew there.... will see how it goes. thanks

Is your wardrobe on the north side of the house by any chance?
I found my wardrobe getting mildewed, happened very winter until we had cavity wall insulation put in. Never had it again. I assume that the outside cold is now not getting through to the wardrobe and it remains warm and dry enough.