Alan Johnson has refused to back down over calls for a cancer patient to be allowed to pay for top-up drugs without having her NHS treatment stopped.
The Health Secretary said permitting her to do so will effectively lead to a two-tier health service.
He was responding to reports that a former nurse, Colette Mills, will be denied free NHS treatment for breast cancer if she seeks to improve her chances of surviving the disease by paying privately for an additional drug.
Mrs Mills, 58, wants to supplement her treatment with Avastin, and has said she is willing to pay the £4,000 a month drug bill herself.
But NHS chiefs say that if she does, she will be classed as a private patient and as a result she will become liable for the entire £15,000-a-month bill for the drugs and care which are currently provided free by South Tees Hospitals NHS Trust.
At question time in the Commons, Mr Johnson said: "You are either a private patient or you're an NHS patient.
"You can be a private patient and then decide to resume your treatment as an NHS patient."
But he added: "You cannot in one episode of treatment have someone who is treated on the NHS and then allowed as part of the same episode, as part of the same treatment, to actually pay money for more drugs."
"No, I do not agree with Mr Johnson. The NHS should provide the treatment, especially as this person as a health professional herself is very knowledgeable about treatment outcomes. If the NHS cannot afford to prescribe the drug but acknowledges that this would be very beneficial, then a client should have the right to supplement drug charges to benefit her best possible chances of long-term survival. If Mr Johnson was in the same boat aiming for his survival with rudder and paddles, would he be using the treatment to increase his chances?" – Name and address supplied