Ferguson is acutely aware that, at 71, nothing can be taken for granted.
"This question (how long will you go on?) comes up more and more because I get older. It is a fact of life. I can't avoid that," said Ferguson.
"It will definitely be me (who decides). The issue is how I feel in myself.
"As you get older, you are not guaranteed your health, no-one is when they get into their 70s.
"I just touch wood that my health remains for a long time yet.
"At the moment, it remains hunky dory. You never know. We are all vulnerable to age. That is the question. How will I be in a year, two years, three, whatever."