Paul Flynn described the present law as "barbaric" and said the government was being "callous" in ignoring the pain of people who could benefit from the drug.

His 10-minute rule bill will go before the House of Commons on Wednesday, the day after a Welsh grandfather who suffers from arthritis was jailed for a year for possessing cannabis.

Mr Flynn told BBC News Online: "I know the man, he's written to me over the years, and it's a barbaric sentence.

Paul Flynn: "The government are afraid of tabloid headlines saying they're soft on drugs"

"But it's not the fault of the courts, it's the fault of Parliament because the judges rightly say if you want to get the laws changed go to Parliament."

He pointed out cannabis had remained in use as a prescription drug in Britain until 1973, while far more dangerous and addictive drugs continued to be given medically every day.

"Doctors prescribe heroin in huge amounts and many of us might very well be grateful for it at some time in our lives if we're in terrible pain.

Paul Flynn: "Law is barbaric but it's Parliament's fault"

"But cannabis uniquely is a very mild drug. It's been used for 3,000 years. We know that Queen Victoria used it for what she called her menstrual cramps.

"It's only been illegal since the 1920s in this country and it's been one of the world's oldest and safest medicines because it's been abused as a recreational drug."

The bill put forward by the MP for Newport West follows recommendations set out by a House of Lords Science Select Committee, which recommended prescribing cannabis.

Their findings were backed by the Multiple Sclerosis society, although the British Medical Association expressed reservations.

The report was immediately rejected by the government. It said cannabis would remain a totally banned drugs while tests into its medical uses continued.

Mr Flynn said: "The government are afraid of having tabloid headlines saying they are being soft of drugs.

"But what they are being is very hard indeed on seriously ill people who've had more than their fair share of life's misfortunes.

"It's heartless - people don't need the medicine in five years' time they need it today. It's callous of the government not to say, you use it, your an adult, it's your own risk.

The MP said he had received an overwhelming response on the issue through his extensive Website.

"There seem to be a lot of people who are aware of what is going on," he said.

"I've had very sad and touching cases of people who say, 'I've got this awful problem. The only thing that works is cannabis. I can only take it in the most dangerous form, which is smoking. If it became legal I could take it in other ways and I could get it from a doctor rather than a criminal trader in the street.'"

Although Mr Flynn's bill stands almost no chance of becoming law, he insisted the law would soon change.

"Last year I had a successful 10-minute rule bill on another subject, so 10-minute rule bills can come into law. There haven't been many.