Do holiday makers visiting this country pay for our nhs services and if not, why?

Obviously we have to take out health insurance to visit other places and we all know america in particular will not treat without first seeing your insurance details. if an american visiting this country takes ill here, do we claim the costs back from them.
Answer
Yes an american is required to pay up front for treatment and claim it back of their insurance.my fiancee was ill whilst visiting the uk a few years ago and went to the local gp. the cost was £20, which she had to pay up front. the receptionist was apologetic about having to take money off her.