Found this info for you Queenie: Plumeria that grow in crowded, humid or shaded conditions are susceptible to powdery mildew, a form of mould. The signature symptom of powdery mildew is white or grey powdery spots on the upper sides of plumeria leaves. The spots sometimes appears on flowers, buds, the undersides of leaves and new shoots. As the infection progresses, the leaves turn yellow, become distorted and drop off prematurely, and flower buds fail to open. The fungus overwinters in brown or black fruiting bodies.

Thanks for your kind help, I've added a pic, but it's not very clear. The spots don't seem to be powdery or mildew and the pot has only been on sunny window sills since Jan when it was bought, this according to planting instructions.
Thanks again, but I doubt it will survive, but it was always going to be a long shot....Best wishes Q...

I hope you can treat it & that it will survive. Might be worth treating anyway as leaves can be affected by fungus, mould and rust & are best sprayed with a copper based fungicide and white-oil solution. At least if it is one of those you will have done your best.