im not an expert on windscreens sarah and i wouldve thought it would be virtually impossible to remove a scratch from a windscreen,,im assuming by what you have said though that you have had a chip in your windscreen and someone has repaired it??if this is the case then they inject like a silicone filler into the chip to stop it from spreading and you ending up with a huge crack in your windscreen,,, most insurance companies cover this work for free and it dont affect your claims as they do not want you claiming for a full windscreen,,,makes sense....anyway...if this is the case then maybe the guy has left some crud on your windscreen somewhere and when you have used your wipers in the rain its spread all over and made it smear,,other than obviously washing the window with lots of hot soapy water which dont always work you can try buying some windscreen cleaner from halfords or wherever as this gets rid of any oily deposits on the screen,,,,dont forget to give your wipers a good clean as well which can be the difficult part as whatever is on your screen is obviously on your wiper blades,,,you will be surprised at how many people simply clean their screen with this stuff and forget about the blades and then wonder why it has not worked lol,,,,good luck

Thanks for the advice. Itwas a long but not deep scratch that was polished out using a compound similar to Jewellers Rouge (i think). There scratch is no longer there but as I said the repaired area behaves differently. In misty rain the rain stays on the polished area more, and in heavey rain the polished are is clearer leaving the rest of the screen appearing smeared/misty.