Ford Focus remove wax on windscreen

Ok, not only in this car, it happened in my old landy. In the dry, no probs, can see fine. At night its ok too, but when it rains and is dark you get like "smears" across the screen, im guessing its wax of some cind, like the jet wash ones that somones sprayed overt the car. It only smears as the wipers go over the screen, goes about 2 seconds later, but when its raining hte wipers live on!

On my old landy I tried that "glass polish" stuff.. didnt do jack. I have tried liberally washing with quite concentrated windscreen washer fluid, no change.

Does anyone else have this problem or had it in the past? Any ideas on how to get rid of the stuff.

Apart from that the screens good, no chips, scrathces or anyhting.

(ps its not mist as happens when have the heated screen on and the hot blowers on the screen)So im guessing it must be some kind of waxy deposit.