The government has confirmed that private patients are entitled to treatment on the NHS.
The clarification came in the wake of a row sparked by South Gloucestershire PCT's refusal to pay £8,500 to continue a 74-year-old woman's migraine treatment.
Maureen Alden, from Bristol, had reportedly spent £13,000 on an operation to implant wires into her brain to prevent migraines, but the PCT refused to pay a permanent replacement battery after the old one ran out.
Lord Robert Winston sought details from the government on this case and others he knew of where IVF patients had been turned down for treatment because of previously having private care.
Baroness Thornton, for the government, said: "When a patient who has previously been receiving private healthcare seeks help from the NHS they should be treated in the same way as any other NHS patient and offered treatment based on their clinical need.
"Their previous status as a privately funded patient should as far as practical neither disadvantage them or allow them to access NHS care in a preferential way."
She said that South Gloucestershire PCT does not routinely fund the treatment referred to, but she agreed to look into the issue.
Lord Winston said: "Many IVF patients will be deeply grateful to you for the statement you have made because I know of a number of cases where unfortunately individual NHS clinics have turned patients down on the grounds that they have had private IVF care before."