A prescription is a legal document for which the prescriber, who has issued and signed it, is responsible.
Prescribers can only provide a private prescription for their NHS patients in circumstances where the medication is not prescribable on the NHS.
A private prescription is not paid for by the NHS, the cost is met wholly by the patient, and is dictated by the cost of the medicine plus an additional charge by the pharmacy supplying it.
A doctor you see privately cannot issue an NHS prescription. If a patient wishes to be referred privately, all costs resulting from private consultations are payable by the patient. This includes prescribing costs.
In some circumstances, for example, to treat a newly diagnosed long term condition with medication routinely prescribed in primary care, your GP may be able to prescribe for your condition, however, they may wish to substitute the prescribed medication with a therapy they are more familiar with, or in accordance with local prescribing policies, to enable safer management of your condition.
Greater Manchester guidance: prescribing following a private consultation