I don't think its actually checked, because every time I fly out of Manchester there is at least one upgrade offer. Either for the Manchester - Paris/AMS or onwards. When I upgraded on check in the app crashed, when I tried again the offer was gone (except for the Man - Paris flight). I tried one more time and it appeared again, and booked it immediately. I had also booked this ticket in the cheapest fare for £380 return during the WOW sale a few months back. Will keep you posted if there is another upgrade offer.