Cannabis-based drugs could be made available on the NHS within two years, the Department of Health has announced.

With the Medical Research Council already conducting studies into the effectiveness of cannabis-based medicines, ministers have asked the National Institute for Clinical Excellence to assess whether cannabis-based drugs should be prescribed on the NHS.

The results of the MRC trials are expected by the end of this year, and the conclusions will be used by NICE in their consideration of whether the drugs should be made available.

A decision on the official licensing of the drugs is then thought likely to follow some time in 2004 or 2005.

The drug is said to have beneficial effects for MS sufferers, those with arthritis and HIV/Aids.

Health minister Lord Hunt said the drugs would only be made available if they proved an effective treatment.

"I think it's important to make a distinction between the drugs for MS pain relief and the use of cannabis for smoking, for pleasure," he told BBC Radio 4's Today programme.

"Of course, the home secretary will have to come to a view on these issues in the future, but what we're talking about here is a proper process, first for the licensing of medical products and then decisions about whether the NHS should make those products available for NHS patients," he added.

Backing for the medicinal use of cannabis could open the door for David Blunkett to effectively decriminalise the drug by issuing guidance to police forces recommending an informal warning be issued for those caught carrying the drug for personal use.

Blunkett is said to have told aides that he will look closely at plans to relax laws on cannabis but has vowed to stand firm against calls to reclassify ecstasy.

The home secretary has already announced that cannabis is being downgraded from a Class B to a Class C drug. While those carrying it would still risk a possible two-year jail sentence, a pilot programme in Lambeth, South London, where police officers issue informal warnings to those caught in possession is thought to have proved successful in allowing the force to target harder drugs.

The Commons home affairs committee is shortly expected to add its voice to calls for the decriminalisation of the drug.

Reports suggest that a seven-month investigation by the committee will conclude that ecstasy should be downgraded from Class A to Class B and prosecutions for possession of cannabis should be scrapped.