Windscreen fogging at night

[Jungle28]

My wife owns a 2012 Ford Focus Hatchback, in the last 12 months, it has started fogging on the windscreen really bad, no water leaks, no damp spots, no musty smell or sweet smells from the air con. Now the car can be sitting for days, no driving and it still does it, have been to several places to ask questions but no one can give me an answer to why this is happening, seems to start at the bottom left and right of the screen??? but there is nothing there that I can find to cause this??? getting really frustrated with this problem ☹☹

Any ideas of what could be causing this???
Thanks