Mrs Ivol said the drug was proved to relieve pain

The study, which is being run by the Medical Research Council (MRC), aims to find out if the drug really can help to relieve pain.

But Ms Ivol, a wheelchair-bound Multiple Sclerosis sufferer, said that clinical trials into cannabis had been conducted by every government for more than 30 years.

The 55-year-old, who lives on Orkney, takes cannabis to relieve the pain of MS and has campaigned for the drug to be made legal.

Successive governments

She was taken to court earlier this year accused of supplying cannabis to others but the case was dropped on the grounds of Ms Ivol's health.

She said: "It just feels like another delaying tactic, saying they have got to do clinical trials.

"I've got files full of clinical trial results going back to 1970.

"They have done these clinical trials over and over again and it seems that every successive government uses the excuse that you have got to wait for clinical trial results.

"I can name a professor not too far away from me who has been doing clinical trials since 1970 with cannabis and MS."

In the new MRC trial, scientists will randomly select 400 patients who have undergone surgery from 36 hospitals across the UK to take part in the study.

Some patients will receive cannabis-based medicines

Researchers will ask the patients about their pain and general well-being at least once every hour while they are awake, over a six hour-period. The patients will be able to request additional pain relief at any time.

Ms Ivol said: "They must realise that there are thousands of people with loads of different illnesses right throughout Britain using cannabis for pain relief. Why don't they just ask them?"

She said painkillers prescribed by doctors have nasty side effects and can kill people.

"I don't see why people can't just grow the plant and use it as they want it."

"Cannabis has never killed anybody and they do know it is a very effective pain relief", she said.

"The only trouble with using cannabis is that you never know how strong it is going to be. Because every time you get it, it is a different plant from a different country.

"It would be lovely to have it regulated so you know what strength you are using."