An undercover investigation by 5 live Investigates has found an unlicensed blood product being sold illegally in the UK to treat cancer.
'GcMAF' is an injectable product made from blood which was offered for sale at a health food shop in Bournemouth.
Cancer Research UK say the evidence for GcMAF is "scientifically extremely dubious".
The BBC has handed a file to the medicines regulator, the MHRA, which is now investigating.
In the UK it is illegal to sell an unlicensed medicine.
No evidence for GcMAF
5 live Investigates received a tip-off that the unlicensed product was available from a man called Nick Greenwood, who works at Earth Foods, a health food shop in Bournemouth.
An undercover reporter posed as a customer seeking GcMAF for a relative with cancer, and was told: "It is one of the best ways to try and tackle it".
She was offered a month's supply for £600 and told the product would need to be taken for six to 12 months.
Patients are told to self-inject 0.5ml of GcMAF every four days, and spray the product under the tongue twice daily.
The Medicines and Healthcare products Regulatory Agency (MHRA) told the BBC that GcMAF is "an injectable blood product, the source of which we have no knowledge. We take this issue very seriously".
Peter Johnson, chief clinician at Cancer Research UK and a professor of medical oncology, warned there was no credible evidence to support the claims made for GcMAF.
He said: "The papers that have been published about GcMAF are scientifically extremely dubious and several of them have been retracted after publication because of doubts about the evidence that they presented.
"If it was me, I wouldn't take it," he added.
'You need to spend more'
At the small high street shop in Bournemouth, surrounded by shelves stacked with herbs and homeopathic remedies, Mr Greenwood told the BBC reporter about five cancer patients who had taken GcMAF, and none had reported side effects.
He said that two of them, who had late-stage cancer, had died.
He implied that they had not taken enough of the product, saying in his opinion: "You need to spend more".
Mr Greenwood took a medical history from the reporter and said it would be passed on to the shop's supplier - a British woman called Amanda Mary Jewell, based in Mexico.
He told the BBC the GcMAF would be dispatched from Bulgaria, via Surrey, and he would take the payment.
After the consultation the undercover reporter received a treatment "protocol" from Amanda Mary Jewell and an email in which she claimed to have been "100% successful thus far at eradicating brain tumours", using a combination of GcMAF and other non-conventional therapies.
In a follow up telephone call, Nick Greenwood advised using GcMAF over medical treatments saying: "What other way is there to go? I definitely don't recommend chemotherapy. And there's nobody in the world of natural medicine that does."
Nick Greenwood encouraged the reporter to take her ill relative to Amanda Mary Jewell's clinic in Puebla, Mexico.
Treatment there costs $4,000 (£3,280) for a 21-day stay.
Amanda Mary Jewell admits that she is not a doctor, but says she has worked alongside medical professionals for 15 years.
She says she does not sell GcMAF from the UK, and claims not to make a profit from GcMAF.
She told the BBC: "Patients come to me when the chemotherapy has failed, when the radiation has failed".
She believes chemotherapy does more harm than good, calling it "mustard gas" and claims: "We get results. People actually walk out of here alive, when the medical industry in the UK have failed, completely failed."
'Snake oil'
Prof Johnson said he had great concerns about people offering completely unproven treatments in return for money, which he described as "a very dubious practice."
"These are very vulnerable people with horrible illnesses who need all the help that they can get, and they need that help on the basis of sound scientifically-based rational advice, not smoke and mirrors, and not snake oil," he said.
"We have treated and cured many hundreds of thousands of people over the years with a variety of types of cancer, using chemotherapy, and there's a lot more people who've had benefit in terms of prolonging their life and improving their symptoms.
"So for somebody who doesn't really understand it and hasn't really been involved with doing it, to simply say you shouldn't take chemotherapy just strikes me as irresponsible," he added.
GcMAF is also marketed at the parents of autistic children.
Autism campaigner Fiona O'Leary is trying to stop it being sold and says she has seen cancer patients reject the advice of their doctors in favour of the treatment offered by Ms Jewell.
'False hope'
Patients of Amanda Mary Jewell appear in online video testimonials, reporting remarkable recoveries.
But sadly several patients who believed they had been cured have since passed away.
They were terminally ill and there is no way of knowing the effect of the GcMAF.
Fiona O'Leary says while she has no information on how they died, she believes they had been given "false hope, because none of it is proven".
She thinks their time and money would be better spent with their families, saying "nobody knows what's in those vials, these people are handing over so much money."
One woman told the BBC she turned to GcMAF when her breast cancer spread to her liver and lung, buying it from a different supplier.
She spent all her retirement savings - Can $15,000 (£9,350) - but her cancer progressed.
She said that with GcMAF "You're blindly putting your faith in something which is not proven".
She has now started chemotherapy and says her tumours are shrinking.
A MHRA spokesperson said: "Medicines need to go through clinical trials to make sure they are safe, to make sure that the quality of the medicines is assured, that the supply, storage and distribution is done properly.
"We can have no assurance this is happening in this case."
"We advise members of the public not to buy unlicensed medicines from unregulated sources and have recently launched a campaign to help people purchase medicines safely," he added.
5 live Investigates is on BBC Radio 5 Live on Sunday 16 October. Listen online or download the programme podcast.
Ruth Evans - BBC Health News
