Serious concerns have been raised about a controversial vein-widening treatment being offered to people with multiple sclerosis.
An investigation by BBC Inside Out discovered that one doctor carrying out the procedure in Egypt is not licensed to practice medicine in that country.
The BBC understands that in the UK, an NHS GP has been reported to the doctors' watchdog, the General Medical Council, for organising the treatment through his private company at a cost of nearly £8,000.
The operation has been dubbed the 'Liberation Procedure' by those who believe it helps relieve the symptoms of MS, an incurable condition.
It involves inserting tiny balloons into the body via an incision in the groin. The balloons are fed up to certain veins in the upper body and neck, then inflated to stretch the vessel wider.
Some patients also have small metal tubes - or stents - inserted to prop their veins open.
The treatment is based on a new and unproven theory that MS is caused by vein blockages which impair the flow of blood from the brain.
This is a radical departure from the mainstream view that there is no known cause of the disease.
It is thought that several thousand people with MS may now have been "liberated" at private clinics in countries like India, Poland and Bulgaria.
Some have posted before-and-after internet videos showing their apparent improvements.
But the MS Society says these results could be down to the placebo effect and the fact that multiple sclerosis symptoms can come and go over time.
Dr Doug Brown, head of biomedical research at the MS Society, says: "One of the complicating factors is the placebo effect where people feel better for going through a treatment process but not necessarily because of the treatment directly.
"It's an unproven treatment and until this treatment goes through a clinical trial it is impossible to say if its works and if it is safe for people with MS."
Blocked veins theory queried
The theory that blocked veins cause MS was put forward just over two years ago by an Italian doctor Paolo Zamboni.
His research seemed to show that only people with MS had multiple abnormalities of certain veins in their upper body which impaired the flow of blood out of the brain.
He called this supposed condition chronic cerebro-spinal venous insufficiency or CCSVI. He said it never occurred in the healthy people in his study.
In 2010, a US researcher claimed that he had found CCSVI in just over half of people with MS. This work has not yet been published.
However seven published studies by independent researchers have failed to back up Zamboni's findings.
Some of those research teams have suggested that what he interpreted as abnormalities were in fact normal and harmless anatomical variations found in everyone.
John Zajicek, Professor of Clinical Neuroscience at the Peninsula Medical School in Plymouth, said: "I can understand that people get desperate. But there's virtually one new treatment a year that people with MS get led into and proves to be ineffective.
"At the moment there's no evidence to my mind that this procedure and this explanation for multiple sclerosis have any value at all."
Concern about treatment risks
Because the theory remains unproven, the procedure is not available on the NHS.
There are also concerns about the risks. Two deaths have been connected to Liberation abroad. Both of those patients had stents which are believed to increase the risks of complications.
Nonetheless, vein widening - without stents - is now being offered in the UK by a Glasgow-based company called the Essential Health Clinic.
BBC Inside Out presenter Sam Smith went undercover to be scanned by Essential Health - the first stage in the treatment process which in total costs just under £8,000.
She was diagnosed with CCSVI.
London-based vascular surgeon Ian Franklin said of Sam's diagnosis: "This reinforces the concern a lot of people have that some of these anomalies might be present in the normal population and raises the question that it might not be specifically linked with MS."
Essential Health is run by a practising GP Dr Tom Gilhooly. He denies any wrongdoing.
Dr Gilhooly insists the Liberation procedure is supported by sound scientific evidence.
He told the BBC: "You are not going to change what we do, you're not going to change our determination to make these patients better. I see these patients, I know these patients, I value these patients, I've looked after them for years. I've seen them after the procedure, the vast majority are improved."
Asked why he thought he had been reported to the GMC, he said he knew nothing about the complaint.
British patients seek treatment abroad
Essential Health has a long waiting list and some British patients are seeking treatment abroad.
Dr Tariq Sinan from Kuwait carries out the procedure on patients from all over the world at a private clinic in Alexandria in Egypt where they do not use stents.
He says he has seen amazing improvements in the patients he has treated.
The Inside Out team travelled with MS patient, Karen Lewis, from Devon, to Egypt.
But shortly before Karen's operation he admitted to the BBC crew that he is not licensed to practice medicine in Egypt.
Karen agreed to him carrying out the procedure anyway.
Two months later, she says her walking and the feeling in her hand have improved - and she is convinced the operation was worthwhile.
She said: "It's like a whole weight has been lifted. Whereas before I used to shed a tear every day, I haven't cried since I had the procedure.
"If this is placebo, I'll take it every day."
This programme is broadcast on Inside Out South West on Monday 7 March BBC One at 1930 and nationwide via the BBC iPlayer following transmission.