Rationing is never a popular exercise, and never more so than in medicine. The idea that the NHS is universal and free has become so deeply ingrained that nobody is happy when it denies treatments on grounds of expense.

The extent of that unpopularity has been highlighted over the past fortnight. First, the National Institute for Health and Clinical Excellence (NICE), which decides whether therapies are sufficiently cost-effective to be provided by the NHS, ruled against four kidney cancer drugs. Though they cost £24,000 per patient a year, and are proven to extend life, they were found to offer insufficient value for money.

This week, the charity Rarer Cancers Forum revealed that one in four cancer patients is denied similar life-extending drugs. The reason was that NICE has ruled against these treatments, or has not yet considered them. It can take up to 18 months to review a new drug, chiefly because of bureacratic delays while ministers decide which treatments they will ask NICE to consider. While they wait, patients must appeal to NHS trusts if they want these medicines, and many are refused.

Both stories have angered patients and doctors. Jonathan Waxman, Professor of Oncology at Imperial College, London, called in The Times for NICE to be abolished, and Professor Karol Sikora, another senior cancer specialist, described the renal cancer decision as a tragedy.

It is easy to understand why they are so upset. The kidney drugs prolong survival by five to six months, and many patients do not respond to the only alternative. While they are expensive, the cost does not appear prohibitive. They are widely available from health systems elsewhere in Europe. There seems no good reason why they should not be a standard option here.

To judge from the genuine shock of oncologists, the decision may yet be revised - as has happened for several other drugs that NICE originally rejected. Yet even if this ruling turns out to have been misguided, NICE is going to have to make more tough choices of this nature. The reason is that the increasing success of medical research will make rationing an ever- greater challenge for the NHS.

Like it or not, there is not enough money to provide, free at the point of use, every medical treatment that people want. There is not even enough to provide every therapy with proven clinical effectiveness - that is why NICE has to consider cost-effectiveness as well.

As knowledge of the molecular and genetic mechanisms of disease increases, this situation is likely to worsen. More and more treatments will become available. Some will be personalised for a small group of patients and will thus be expensive because the market is limited. Others may extend life only for a short period and will offer poor value for money on the NICE model. Some will have to be rejected for NHS use, even though they work.

At present, this means in practice that most patients are refused them altogether.

If they choose to buy a non-approved drug privately, they must then opt out of all NHS care: so-called co-payment is not allowed. While a drug alone might be within a patient's means, an entire package of private healthcare is often not.

This situation is under review and a decision is expected in the autumn. It is hard to see how the status quo can remain. As science delivers powerful but expensive medicines, patient demand will outstrip NHS supply. NICE will rightly reject treatments that prolong life by a month or two, but many patients who cannot afford hundreds of thousands of pounds for wholly private care will nonetheless want to pay tens of thousands, on the principle that you can't take it with you. There is legitimate concern that such co- payments will introduce a two- tier NHS. However, the fact that not everybody may be able to afford to top up their treatment does not mean it should be denied to those who can.

Mark Henderson is Science Editor of The Times

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