The Medicines and Healthcare Regulatory Agency (MHRA) met last week to discuss Sativex, a medicinal form of cannabis.

It decided more clinical data was needed before the drug could be approved for treating muscle stiffness in MS patients.

Professor Mike Barnes, consultant neurologist at the University of Newcastle and a trustee of the MS Trust charity, said: "This decision leaves many people with MS little option but to resort to 'street' cannabis for relief from the painful and disabling symptoms of their condition.

"With Wednesday's announcement by the Prime Minister that re-classification of 'recreational' cannabis is being considered, this is even more worrying."

He said there was "compelling" evidence that Sativex helped a large proportion of people with MS.

On average, half the patients who tried the drug gained some benefit and there were no concerns.

Chris Jones, chief executive of the MS Trust, said: "It is a sad fact that the system imposes a 'one size fits all' model on a condition like MS. One size never fits all with MS - it is a hugely variable condition with variable responses to treatments. To deny some patients because the treatment doesn't help everyone is madness."

A fifth of 160 people surveyed by the MS Trust had reported a reduced need for supportive equipment or mobility assistance, said Mr Jones. Almost everyone taking part experienced an improvement in general life benefits.

"Sativex meets a currently unmet medical need in patients where there is no other conservative treatment option," said Mr Jones. "It is our view that Sativex should be licensed and become available on prescription."