How do I know? Well, from personal experience, from seeing and listening to what people have said over decades in polls and surveys, from petitions to save the NHS. There are countless indications. As pointed out to Derek, I have never heard anyone suggesting it to be taken away from the state.
Sure, many people criticise the way it's run, and the gradual privatization is terrible, as was the pfi scheme. But out of the state's hands to become what? Where would the money come from to build new hospitals? Who would be in charge of that money? It will be a great for the corporations ready to "provide" private health care.