From a friend of mine who had the unenviable job of working in a large airline complaints department during the Volcanic Ash episode. When Scottish airspace opened temporarily in the middle, he had the following discussion.
"It says on the news that Glasgow will be open tomorrow so why is my flight still cancelled. Why can't we go from Glasgow?
"Because unfortunately, Heathrow airspace will still be closed Madam and the aircraft is at Heathrow.
"Yes but Glasgow will be open. Why can't you transport us by road to Glasgow and we can meet the plane there?"
"Because Heathrow Airport is closed Madam and as I said, the plane is at Heathrow"
"Yes, I know! That's why you need to fly it to Glasgow, which will be open, so we can get our flight!"
"You really aren't getting this are you, Madam?"