Went out to the car this morning to find both windows all the way down. I know for a fact that they were closed when I got home last night. The windows do not open when you hold the unlock button on the key.

So my question is why would they have gone down

Our old Mk 1 Octy used to drop all four windows of it's own accord, quite often overnight and/or when raining!! Never did get to the root of the problem so ended up px'ing for our current Fabia (manual system so no problems there).

It's the lock and barrel in the drivers door sticking. If you turn the key and hold it all the way to the right the windows go down. They have a habit of getting mucky and sticking. Get it out and clean it up and it should be fine after that.

Had this on mine and it turned out to be the drivers electric door lock needed replacing

Had this on mine aswell, about 2 yrs ago, but only the drivers window. It's never happened since ( touch wood ) but the nite it happened it snowed. Needless to say, I had about 3" of snow inside the drivers side of the car. Not impressed.