taken from wiki..
The National Health Service or NHS is the publicly funded healthcare system in England. It is both the largest and oldest single-payer healthcare system in the world. It is able to function in the way that it does because it is primarily funded through the general taxation system, in a similar fashion to the funding model for fire departments, police departments, and primary schools. The system provides healthcare to anyone normally legally resident in England, and also any other part of the United Kingdom (should a person from another UK area be travelling in England, for example), with almost all services free at the point of use for all such people.
The idea of the NHS being free at the point of use is contained in its core principles from the original NHS set-up, which are non-negotiable at their root but have variously been open to some interpretation over the years. In practice, "free at the point of use" normally means that anyone legitimately fully registered with the system (i.e. in possession of an NHS number), including UK citizens and legal immigrants, can access the full breadth of critical and non-critical medical care without any out-of-pocket payment of any kind. Some specific NHS services are fee-for-service: since 1948, patients have been charged for services associated with eye tests, dental care, prescriptions, and aspects of long-term care. However, these charges are often lower than equivalent services provided by a private health care provider.
I work in the NHS and we also treat all patients but patients need to be registered with a GP, have an NHS number to be able to get the free health care lets say, but overseas patients and private patients have to pay for treatment.