You're still entitled to free NHS care if you choose to pay for additional private care.
The Department of Health has published guidance for NHS patients who pay for additional private care (PDF, 126kb). The guidance says:
The guidelines state you should receive your private care at a different time and place from your NHS care whenever possible.
This means private care should ideally be provided in a separate building to NHS care or, if an NHS organisation also provides private care:
Occasionally, a patient's doctor may agree they can receive their NHS and private treatment in the same place – for example, if the doctor decides the patient is too ill to be moved.
If you're receiving private and NHS care for the same condition, your NHS and private treatment can be supervised by one healthcare team.
You cannot choose to mix different parts of the same treatment between NHS and private care. For example, you cannot have a cataract operation on the NHS and pay privately for special lens implants that are normally only available as part of private care.
Instead, you either have to have both the operation on the NHS and standard NHS lens implants, or pay for both the operation and implants privately.
You shouldn't need to have any of the same tests twice – for example, to diagnose or monitor your condition. In this case, the test will probably be part of your NHS care and the result will be shared with your private care provider if necessary.
Your doctor will tell you about all the treatments for your condition, including any that are only available privately.
If you want to know whether your doctor can treat you privately, you will need to ask directly. They can then tell you about the private services they offer – for example, cancer medicines or other medicines not funded through the NHS.
Your private healthcare provider will normally treat any non-emergency complications that result from the private part of your care – for example, you might have side effects that need extra treatment.
You'll need to pay for this treatment yourself. However, the NHS should never refuse to treat patients because the cause of the complication is unclear, and should treat any patient in an emergency.