But while GW's genetically unique cannabis plants might leave you frustratingly sober, it is their non-psychoactive properties that are altogether more interesting.

For a decade, GW has been developing Sativex – a medicine derived from chemicals in cannabis, known as cannabinoids, which have been shown to ease the muscle stiffness associated with multiple sclerosis.

Despite the closely-monitored production process, the road to regulatory approval has been rocky. In 2005 Sativex won clearance in Canada for the treatment of neuropathic pain, making it the world's first cannabis medicine to get the green light. Approval in Europe, however, has been hit by a string of regulatory delays.

But last Friday GW confirmed that the Medicines and Healthcare Products Regulatory Agency in the UK had finally given Sativex the go-ahead. Approval here should be followed by Spain and other European countries. Analysts at Piper Jaffray forecast that peak sales could reach £121m in Europe and Canada combined.

Speaking in the weeks prior to MHRA's decision, when GW knew the regulator had no major issues with Sativex, Mr Gover told The Daily Telegraph approval in the UK would mark the culmination of "a great deal of effort".

"MS is a very difficult condition to study in clinical trials so this has probably been one of the most complicated developments undertaken by the industry," he said.

GW was founded in 1998 in response to concerns about MS patients who risked prosecution when they smoked cannabis to try to help ease pain and muscle stiffness.

"Everyone knows there are patients who see [smoking cannabis] as their only effective treatment option. The patients know, the Government knows and the reason for this is not because people with MS decide they wish to smoke joints," said Mr Gover. "They are in the unfortunate position of doing so because medication in MS treatment is poor – there's been no innovation for decades."

In the late 1990s, he added, it became clear that the Home Office was receptive to finding a legal medicinal solution for these patients. Against that background Dr Geoffrey Guy agreed to establish a company to look at developing a prescription cannabis-derived medicine that would meet the rigorous standards of regulators.

A Home Office licence to conduct the research was granted in 1998 and GW was born. But even then, funding was hard to come by, says Mr Gover – who joined GW, where Dr Guy is now chairman, in 1999.

While trials have shown that Sativex helps reduce spasticity in MS patients, it is not the only condition that GW's cannabis plants could potentially help to treat. GW has also discovered therapeutic potential for schizophrenia, epilepsy and types of diabetes.

For now, GW is delighted at having finally got the UK regulatory green light. "Sativex is not going to cure MS," says Mr Gover. "But what this medicine can do is it makes your life tolerable again. It doesn't work for everyone - it's not a miracle - but it is a worthwhile innovation and we're genuinely delighted."