By Branwen Jeffreys
Health correspondent, BBC News
Cancer doctors have told the BBC they fear the NHS will not be able to afford the new generation of cancer drugs.
Many cancer charities are concerned about the issue of drugs
Specialists are already arguing that patients may have to pay for more drugs themselves, with the issue becoming pressing as new drugs are developed.
But some patients offering to pay for a cancer drug are being told they would have to meet all their care costs.
It is due to different interpretations of contracts and policies designed to separate private from NHS-funded care.
The issue is becoming more critical as the number of new cancer drugs being developed grows.
In all, 180 specialist cancer doctors told the BBC they were worried or very worried about the situation, in response to a questionnaire submitted by the BBC.
Around half the drugs submitted to the English NHS advisory body NICE are for the treatment of cancer.
Some, like Herceptin for breast cancer, have won NICE backing as being cost effective for the health service. Others like Tarceva, which can extend the life of lung cancer patients, have been turned down.
Specialists like Nick James, professor of clinical oncology in Birmingham, believe the gap between what the NHS can fund and what is available is going to get bigger.
"The drugs in the pipeline are going to cause even more pressure. I think politicians need to be honest and say this gap is going to be there and we need to look at ways of filling it," he said.
He believes it is inevitable that patients will make a bigger contribution themselves, but is worried NHS policy stands in the way.
Some patients who offer to pay for a cancer drug recommended by their doctor are told they will have to transfer completely to private care. This can have the effect of doubling bills which already run into many thousands.
Professor James works in one of a number of trusts which interpret policy more flexibly, effectively allowing patients to pay for cancer drugs and continue to receive other NHS care.
Stephen Allen is one patient to benefit from that, although that still leaves him paying £3,000 every six weeks for the drugs alone.
Mr Allen is terminally ill with kidney and lung cancer and had been told he only had six months to live.
Stephen Allen is paying for his own drugs
NHS funding for the drug recommended for him was refused, with letters explaining the health service has limited resources and faces very tough decisions.
He said: "I didn't realise we had to pay for certain drugs. If they'd said from the start there are certain drugs on the list which aren't available to you, we probably would have understood a little bit easier the situation they're in."
So Mr Allen is spending savings he wanted to leave for his wife in the hope of living to see the first birthday of his youngest grandchild, two-month-old Annabelle.
In England, the official policy of the Department of Health is that allowing patients to contribute towards NHS care - known as co-payment - is against the principles and values of the NHS. The government says it could lead to a two tier system.
In Scotland a different picture is emerging. Earlier this year Scotland's Chief Medical Officer issued much more nuanced advice to the health service there.
He points out that if a patient opts to pay for a particular drug not available from the NHS there is no law which allows health boards to make the patient pay for all aspects of their treatment.
The letter sets out a framework for drawing up ways of allowing "the safe provision of concurrent treatment where appropriate".
The NHS has received a record increase in funding in recent years, but it still has to set financial priorities within those limits.
A government report published by the National Cancer director for England, Professor Mike Richards, said cancer care had improved, with faster access to treatment and money spent on new equipment.
Professor Richards, said demand for drugs would grow, and need had to be met on a fair basis.
"We have got to look at whether we are using the current money on cancer in the NHS as effectively as we can."
But he added: "There are limits to what the health service can pay."
Dr Jesme Fox, medical director of the Roy Castle Lung Cancer Foundation, said she was appalled some people spend the last few months of their life in a desperate fight for NHS funding.
The average time from diagnosis to death for lung cancer patients is six months.
"If they're not going to be allowed to access drugs that improve survival by a few months, or improve their quality of life, we need to have an honest debate about how we're going to have to fund these things."