Hang on a minute.
Accident and emergency care is indeed free. However, lets say you are admitted in an emergency - but it turns out you need treatment for something more long term. The moment you are moved from a bed in the A&E to another department then it becomes fully chargeable, if you are not a UK or EU citizen. Only the immediate emergency care is free - everything else (including any drugs you need) is chargeable.

Also - if your admission is as a result of a road accident, the entire cost (including emergency care) is chargeable. It would be normal for this to be covered by the insurer of the vehicle you were travelling in - but if you were incautious enough to take a "hawking" cab rather than a licenced one it would not have any valid insurance cover.

Also consider (though I sincerely hope it doesn't happen) if you break a number of bones and need specialist transport to get home? The NHS won't pay for that.....