Scotland should open a debate over whether the latest medicines should be prioritised for younger patients over the elderly, the head of Scotland's drug watchdog believes.

Dr Ken Paterson, the new chairman of the Scottish Medicines Consortium - the body which guides health boards on which new treatments to prescribe - also warned that the soaring bill for drugs could bankrupt the NHS.

In his first interview since taking up his post, Dr Paterson said he had attended a number of events where audiences were asked to choose between two medicines of equal cost and effectiveness - but which helped people at different stages in life.

He continued: "Every audience has always voted to buy the drug for a young person. The evidence is people are willing to be ageist. The question is, is that a right or a wrong thing?"

He said the SMC has already specified that some cancer drugs should only be given to patients who in their current condition have a good quality of life. He believes Scotland ought to discuss whether it is willing to spend more on treatments which prolong or improve the life of younger people.

"That is not for SMC, that is a social debate. The sad fact is that there is not that discussion taking place. These are not SMC's decisions. These are decisions wider society has to take and we do not see much evidence of that discussion taking place."

He admitted there would be fierce opposition to the premise, but added: "If it is going to be controversial, at least have the debate."

His comments follow those of leading Scottish churchman, the Rev. Maxwell Craig, Extra Chaplain to the Queen in Scotland, who questioned whether the health service spends too much treating the elderly at the expense of the young. The bill for prescriptions in Scotland rises every year, reaching £998m in 2006-07, and patients are increasingly demanding access to the latest generation of medicines, such as the breast cancer drug Herceptin, which can be expensive to make and purchase.

Dr Paterson said: "I think the NHS will probably continue to say yes to Herceptin. Is there a possibility of being able to have other truly life saving drugs like that which are in danger of bankrupting the NHS? Perhaps. We do not know the answer to that.

"We may be entering that phase and that will be difficult because we have had a substantial funding expansion in the NHS which is coming to an end now and at the very time where there may be really beneficial but really quite expensive drugs in the pipeline. That is why it is all the more important to make sure we are spending the money in the most effective way."

He also put forward two other areas for public discussion: weighing up the importance of improving someone's quality of life against the importance of prolonging their life and the value of treatments which deliver immediate health benefits against those more preventative drugs which pay-off years down the line.

Lindsay Scott, spokesman for Help the Aged in Scotland, welcomed the call to debate the issues, saying the allocation of resources did need to be examined with the ageing population. However, he added: "I would find it very difficult to support any suggestion that younger people should be prioritised over older people. It is our belief that there is enough age discrimination happening as it is." Reports already suggested doctors were more likely to offer treatments to younger patients, he said.

Two more new drugs were rejected by the SMC yesterday, on the basis that their manufacturer "did not present a sufficiently robust economic analysis". They are Paliperidone (Invega) for the treatment of schizophrenia, and maraviroc (Celsentri) tablets, designed for use in combination with other antiretroviral medicinal products, for adult patients infected with only CCR5-tropic HIV-1.

However the SMC also approved three new drugs. Nelarabine (Atriance) was accepted for the treatment of patients with T-cell acute lymphoblastic leukaemia (T-ALL) and T-cell lymphoblastic lymphoma. Methoxy polyethylene glycol-epoetin beta (Mircera) was approved for the treatment of anaemia associated with chronic kidney disease. Vildagliptin (Galvus) was accepted for the treatment of type 2 diabetes mellitus.