"Obviously, the air quality of London meant that we had to consider our patients first and we have to consider the quality of the air that's coming to them, " he said.

BBC: Closing hospital windows 'increases infection risk'

"We knew that his retirement would come one day and we both have been planning for it by ensuring the quality of the squad and club structures are in first class condition, " he said.

CNN: Alex Ferguson retires as Manchester United manager