Misted Windows

[i:7eae3b9d8f]My sovereign windscreen mist's up when I go faster than 70mph. A grey film comes over the windscreen, starting just above the vents on the dash board. I have noticed too, that there is condensation in an arch pattern in the same area and that my drivers mat is constantly damp, also sometimes, what seems like a clear, water like type of liquid drips on my left foot. I have checked for possible leaks and holes all around the car and can't find any.
Can anyone help me with this query as I have made several attempts to find out what might be the cause, but have been unsuccessful?[/I:7eae3b9d8f][/b]