The NHS is not a single object to be sold or not sold. It is a composite that can be sold over time in various ways, such as by extension of patent times which is in the documents, or reducing services in a way that obliges people to go private.

I came across a BMI Healthcare article which starts "Almost two thirds (65%) of people on Britain are not aware that some medical procedures are no longer available to them on the NHS'. (The only reason I don't link to it is that it is is basically a sales pitch for private healthcare.) But there are others: 17 "unnecessary procedures" were dropped by NHS England in June 2018. And so on. If there was some tiny corner tiny corner kept as free at the point of use (and after all, you can make the case that private health insurance is as well) does not mean the rest of the NHS has not been sold.