Parking Eye: Is this legal?

[gammledansk]

I had to visit our local hospital recently. I did not know how long my appointment would be so thought that 2 hours would be fine and duly paid £2.00. The appointment took 2 and a half hours, so I had over ran by 30 minutes approximately. The hospital waiting rooms etc have notices from Parking Eye advising you that should you run over your time, not to worry you can 'top up' on exit. Having been on the receiving end of one of their 'fines' in the past-I didn't pay - but did not want the hassle again- so before unlocking my car I went to the machine and looked at the next charge band: 4 hours @ £3.50. As I already paid £2.00 and was 'topping up' as their notice suggests, I tried to input £1.50. This money was rejected twice, and I had to purchase a further 2 hours at the rate of £2.00. In other words I paid £4.00 because when I entered I did not have any idea how long I would be at the appointment. It is only 50p to me, and neither here nor there But how many folk have to pay the difference when it is NOT a top up.Its extra money in their coffers. Its a con.Is it LEGAL?? I dont want my money back but I think of folk following ambulances in with heart attack/stroke victims to A&E -folk with appointments time being unknown. It makes me so angry. Is there anything I can do?