Ministers are preparing to allow public patients to pay for some top-up drugs in a decision that opponents claim will spell the end of the National Health Service.

Alan Johnson, the Health Secretary, is poised to relax the ban on patients paying privately for life-extending treatments while receiving NHS care. Such a change could result in wealthier patients living longer because they have been able to buy expensive drugs not approved by the NHS. It will force cancer sufferers to consider whether paying more than £30,000 a year for a drug is worth the extra months or years they could gain.

Mr Johnson is aware that such reforms to the ethos of the NHS would be controversial, but believes that the current rules are unsustainable.

Ministers hope that an independent review next month will help to make the case for change. “Whatever is recommended won’t satisfy everyone. There is no magic bullet that resolves this very difficult issue,” one senior figure told The Times.

Professor Richards is expected to legitimise practices that circumvent the current guidelines. Some hospital doctors turn a blind eye to the rules and allow NHS patients to receive privately funded drugs. Any changes would be accompanied by measures to speed up the approval process for new drugs and make them cheaper, aides say.

Reforms are planned to the system under which local NHS committees decide which patients are exceptional cases and can receive drugs not yet approved by the value-for-money watchdog.

Doctors, healthcare unions and some Labour MPs argue that allowing wealthier patients to purchase better care will lead to a two-tier system and undermine the founding principle of the NHS to provide care based on clinical need, not ability to pay.

Those who favour top-ups argue that a postcode lottery already exists where patients in some areas are granted treatments that could extend their lives while others are not.

Ministers were forced to review the ban after an outcry over the death in March of Linda O’Boyle, a grandmother who was denied free NHS treatment after buying a drug to treat her bowel cancer.

The National Institute for Health and Clinical Excellence assesses the cost-effectiveness of new medicines and recommends whether they should be provided by the NHS in England and Wales. Where it has turned down a drug, or has yet to make a decision, patients can appeal to their local NHS primary care trust to be treated as exceptional cases. Niall Dickson, chief executive of the King’s Fund think-tank, said that patients had not been given reasons why some costed treatments, such as dental care, were allowed on the NHS but others were not.

NHS managers say that the current system is unsustainable but that patients must be made to understand what might happen if they ran out of cash before finishing their treatment.

Mr Johnson agreed to reconsider the issue in June after a series of reports about patients who were refused NHS care after buying drugs for cancers of the kidney, bowel, lung, breast and multiple myeloma.

Scotland is conducting its own review on co-payments specifically limited to cancer treatments.

Professor Richards said that he was in discussions with patient groups, NHS staff, pharmaceutical companies and the insurance industry over which patients would be willing to pay for extra care.