Let's just summarise the situation here, for visitors to the UK. I shall use a scenario, to cover a few points.
Someone collapses in the street. An ambulance is called. They are treated at the scene by paramedics ..... free ..... who then transport them to A&E ... free ..... and then they are treated in the A&E ... free .... but then unfortunately they need to be moved to theatre and/or ward ... not free!
In other words, quite when it starts to get really expensive, the treatment is not free. Accordingly it is essential for every visitor to the UK to have adequate travel insurance, to cover possibly rather large medical bills.
So for you, Gottagettolondon, get yourself along to A&E. You will not be charged there.