"car parking at Sutton Hospital"

I think the staff at the eye department are lovely. However, my main concern is you have to pay for the car parking before going into the hospital. I have found on many occasions that you have no idea as to how long your appointment is going to last, hence I tend to often pay for more parking hours/minutes than I need. Why can't Sutton Hospital adopt a fairer way of paying for parking, like at St. Georges Tooting for example, where you collect a parking ticket on entering the car park and pay for the duration of the parking when leaving. Seems to me to be far more practical.