Dr Rosy Daniel is well known among cancer specialists. As the medical director of the famed Bristol Cancer Help Centre, she has spent years trying to change attitudes towards cancer and encourage her own "holistic" vision. With Prince Charles as patron of the centre, Dr Daniel's emphasis on treating cancer by emphasising diet and healthy living, positive visualisation and changing lifestyle, became increasingly well known. Despite many sceptics.

Now Daniel appears to have put her reputation on the line for a herbal remedy that hasn't yet had any clinical trials. She's gone public with her conviction that Carctol, an unlicensed Indian herbal medicine, may be the cancer cure that people are looking for. Her PR team has even issued a release entitled, "Has Dr Rosy Daniel Found the Herbal Cure for Cancer?" It's a question that has enraged many in the medical establishment.

"What on earth is this about?" asks Professor Robert Souhami, executive director of Cancer Research UK. "The idea that this is a substitute for proper intervention is laughable. She's talking a kind of bad science."

Souhami is angry because he sees the claims as the latest in a stream of assertions from alternative practitioners which appear to offer cures for cancer - without backing them up with proper research. "What responsible cancer doctor would follow this up when she hasn't followed it up herself?" he asks. "This makes people in a vulnerable and difficult position feel that they ought to give it a go, but no one should say anything about the results of therapies unless they know what they're saying is true."

Daniel, who now works as medical director of a private company, Health Creation, still treats patients with cancer. Her philosophy remains the holistic approach that she used at Bristol, and she knows the sceptics are out there. "I've been working with integrated healthcare approaches in cancer for 20 years," she says. "I think it's important to keep an open mind and I'm on the side of the patient. That's the bottom line, even though doctors might want to hang me and burn me as a witch."

Daniel's words give an idea of the pressure she's under. But she hasn't helped herself with the way her latest discovery is being explained. Her story was given extraordinary prominence in yesterday's Daily Telegraph under the headline "I've seen herbal remedy make tumours disappear, says respected cancer doctor".

Daniel herself says she is not making a scientific claim for Carctol, but merely observing a phenomenon. "All science starts from hypothesis," she states. "I'm not saying this is the answer, but I have stuck my neck out and prescribed it." Her press release, however, talks of "walking miracles" and quotes Daniel as saying it is "thrilling" to have "finally found a herbal medicine which can be a lifesaver".

The problem is that Daniel has not done any medical trials on Carctol, a mixture of eight herbal medicines. She says she has prescribed it to around 860 patients - about a quarter were helped, a quarter were not helped at all, and around half were helped to some extent. It's hardly a methodical or thorough assessment.

"People who make huge claims but fail to collect the data are irresponsible," says Dr Rob Stein, consultant medical oncologist at UCLH. "We need systematic and rigorous trials, but that's not happening here. Many of my patients do check out complementary therapies. They do it because it empowers them and that's fine. It's a very natural desire of people to help themselves. But whether any of it actually works is very much open to question.

"The difficulty is that we are told about the successes, but not the total number of people taking these remedies. I personally don't believe it, but if it makes people feel better about themselves that's fine. The only thing it hurts is their wallets."

Daniel herself - who explains that it is only possible to receive Carctol on prescription in this country, at around £90 a month - admits that she was unsure when she first heard about the drug. But she then met the Indian doctor who developed the treatment, Dr Nandlal Tiwari from Rajasthan, and she says his results are astonishing.

"When I was director at Bristol we got sent things all the time. But this one has living proof," she says.

The theory is that cancer is connected with acid levels in the body. Taking Carctol - and drinking lots of water, changing your diet and taking a digestive enzyme, all as recommended by Dr Tiwari - makes that acid level more alkaline and stops the cancer from thriving.

"It's complete scientific nonsense," says Souhami. "The body can't be made more acid or alkaline. Acidity is very tightly controlled. The problem for people like me is that you're seen to be some kind of medical fascist who wants to do people down, and that's not true at all. Our culture in orthodox medicine is that everything should be tested. What's difficult about people like Daniel is that she doesn't start from that point. She believes in a general kind of philosophy of cancer."

Souhami is particularly dubious about the recommendations that Carctol should be taken with a changed diet, digestive enzymes and "cooled, boiled water."

"What is it that is actually supposed to be working?" he asks. "How do you test all this out? There's no explanation why the water has to be that particular amount, or why it has to be cooled or boiled. It sounds to me like a triumph of wishful thinking. It's selling a package, trying to make cancer patients feel in control of their body, which is no bad thing, but this is serious for people. You have to be careful."

Earlier this year, Prince Charles was roundly criticised by the cancer specialist Professor Michael Baum for singing the praises of the Gerson therapy, a particular diet which is said to help cancer sufferers.

"I have much time for complementary therapy that offers improvements in quality of life or spiritual solace," wrote Baum, "providing that it is truly integrated with modern medicine. But I have no time at all for 'alternative' therapy that places itself above the laws of evidence and practises in a metaphysical domain that harks back to the dark days of Galen."

For many, Daniel and her treatments are seen in a similar way, despite the claims of her patients that they have been helped by her approach. In fact, Daniel herself emphasises that Carctol can be used with conventional medicine and says she is keen for medical trials to be carried out.

"I have given 20 years of my lifeblood and passion to work and help people with cancer and I'm always happy to be someone there at the edge," she says. "I'm happy for this to be used with conventional medicine, but I've met people who say they would rather die than have chemotherapy. Why not give them a choice, chemo or herbal medicine? Quite often chemo is oversold because there is nothing else. I would hope this is the something else.

"I always get criticism, but if your life was threatened and there was a source of hope, you might want to know about it. I am happy to say that this needs research and it is essential to do trials. But some patients say they can't wait for evidence. They might be dead before it comes through."

Nevertheless, Souhami remains unconvinced. "People with cancer have their hopes hanging by a thread," he says. "It's just not fair to say things work unless you know they do."