The scientists have been granted permission to grow the drug at a number of secret sites in the south of England. The new, "safe" variety is manufactured by extracting the element that gives the "high". The aim is to produce a drug that can be used to treat a number of illnesses including multiple sclerosis.
Botanists have known for years that cannabis contains an element that can bring effective pain relief and campaigners for its decriminalisation have long argued its medicinal properties.
But scientists have now found that the pain relieving elements in the drug have little to do with the "high" that smokers cherish.
In an exclusive interview with the Independent on Sunday Mr Hellawell said the discovery has, at a stroke, destroyed the campaign to legalise marijuana. He revealed that a British company, GW Pharmaceuticals, has been licensed to produce the new, modified drug.
The Home Office decided to back research into using cannabis extracts for medicinal use two years ago. Initial tests to isolate the most beneficial parts of the plant have shown that tetra-hydrocannabinol (THC) - the intoxicating compound in cannabis that gives recreational users a high - is not the element that relieves pain.
Now scientists are developing a cannabis-based drug with a minimal THC content. Trials are already taking place with 660 multiple sclerosis sufferers to measure the therapeutic effect of the Class B drug. The three-year study, costing nearly pounds 1m, is being carried out by the Medical Research Council. If the results are positive, the specially produced cannabis will be available as a treatment on prescription in the next two years in the form of an inhaler.
Mr Hellawell said the Government's policy not to legalise cannabis has been vindicated and emphasised that cannabis in its pure form had a greater carcinogenic effect than tobacco.
"I get cross when the legalisers for recreational use used to be able to say all these poor people are suffering because of prohibitive policies," he said. "We have taken that argument away by carrying out this research. The benefit people may have in dulling their senses may not be the benefit needed to help them with their disease.
"There is no doctor in the world, even the ones who support the use of cannabis derivatives for medical treatment, who would support smoking of cannabis."
GW Pharmaceuticals confirmed that its tests had shown THC to give little benefit, although the company stressed it held a neutral position. "The myth is that sufferers benefit from THC because it dulls the pain," said a spokesman. "We want to develop a dose so there is no side-effect or high. I've talked to MS sufferers who are using cannabis and they have learned how to just take enough so they don't get high. Patients want to get on with their lives."
However, many MS suffers remain sceptical about the trials and intend to boycott any treatment that becomes available. Colin David, a member of the Medical Marijuana Co-operative, started using cannabis after fracturing his spine and has been acquitted twice for cultivating the drug. His view is that the treatment under development would not be as beneficial as cannabis in its pure form.
"The tablets they are using in the trials have been around for a while and have failed before," he said. "There are thousands of components in the plant which work together to benefit sufferers. Isolating only a few elements cannot have the same effect.
"Cannabis should be legalised. It's safer than alcohol and is far cheaper for people to grow their own."Reuse content