Dental and optical treatment can cost a lot of money, but at least staying as a hospital in-patient is free, isn't it?
That's largely true. There are no direct hospital in-patient costs and you won't be charged for your basic care, drugs, nursing or food.
But an overnight stay in hospital as a patient yourself or as the parent of a dependent child that needs you to stay in hospital with them could cost you directly in lost overtime, unprotected earnings or even benefit deductions.
You might also find yourself admitted as a hospital day case for treatment or investigation and then find yourself requiring medical help with your recovery.
Either way it could be a cost that you were not expecting!