You may have seen the direction signs if you drove down to Manchester Airport. The mill and nearby Styal village owned by the Greg family are now owned by the National Trust.
I was there a couple of months ago giving a business presentation when the TV crew was on site. There were extras everywhere having their faces and hands made grimey by the make-up team with trays of what looked like ash. I managed to take a couple of shots from the overhead passageway between filming.