In the heart of Cumbria stands a two-bedroomed cottage wrapped in ivy that for half a century has been home to a lady named June. She makes a pot of tea in a cluttered kitchen brimming with fresh herbs in labelled jars, assorted saucepans and drying socks, then potters across the slate floor, and into a garden. Here lies what June calls "her private retreat". An overgrown rose bush dotted with apricot-coloured blossoms creeps over a rusting bench and from one of the many ceramic plant pots comes the scent of rosemary. At the back of the garden stands a decaying shed, lost beneath a white climbing hydrangea, and nestled behind this sits a small grow tent, which June tells me contains a single cannabis plant. She pulls down the zip to reveal the hidden green leaves. "You wouldn't believe it was only one plant!"

The sight is reminiscent of the film Saving Grace, where an elderly widow starts growing cannabis as a way of paying off debts – but June has no intention of making money from her plant, nor does she plan on smoking it.

Inside, on the mantelpiece, sits a brown envelope addressed to a nearby town. It contains a small bag of weed. "I'm sending this to a friend of mine with arthritis who I've been helping out for a few years," she says. "I promised to have it delivered to her a few days ago but it took me longer than I expected to harvest this time so it's a little late."

June first started to grow cannabis in 2003, after a neighbour gave her late husband, Arthur, a sample. Arthur, who had suffered from MS from the age of 46, had developed secondary progressive MS and severe spasticity – involuntary muscle stiffness and contractions. June says she experimented with different strains of cannabis and found some were particularly effective muscle relaxants.

After seeing the relief it brought her husband, she decided to grow her own and began searching through the wealth of blogs and forums offering guidance. "I don't exactly operate on a grand scale," laughs June, who says she never has more than one plant at a time. "If you look after a plant properly it can go a long way." She initially wanted to set up an aquaponic grow tent, which combines keeping fish with hydroponics – but decided it was too conspicuous. "It's a shame. I already keep fish and it is much more eco-friendly."

"I've got no real interest in the stuff myself. I just really love gardening and I'm glad I can use it for a purpose which helps people." June provides cannabis for three other people: two, aged 78 and 85, who have arthritis and live nearby; the other aged 73, who has MS, to whom she sends cannabis once a month, often in a bag of coffee to mask the smell. "I'm still learning," says June. "The stuff I grow isn't always effective but it does seem to provide some comfort."

Cannabis has been used as a medicine throughout history, with the ancient Egyptians among the earliest users. Its first recorded use as an anaesthetic is in first-century China; the Chinese term for "anesthesia" can be translated as "cannabis intoxication". Increasingly, the medicinal benefits of cannabis are being recognised and researched internationally and growing numbers of countries have legalised it. Recent research from the New York University Epilepsy Centre, for instance, has shown the cannabidiol (CBD) element in cannabis can help reduce epileptic seizures. The CBD-high cannabis strain Charlotte's Web is now in demand in Colorado among individuals seeking help for epilepsy.

Even though, in 1998, the Home Office granted GW Pharmaceuticals a license to grow cannabis in order to develop cannabinoid-based medicines, Britain is not following suit. This week, Norman Baker, Lib Dem minister of state for crime prevention, called for more liberalised drug laws, and specifically the legalisation of cannabis grown for medicinal use. A coalition spokesman rejected his suggestion outright: "This government has no plans to legalise cannabis or to soften our approach to its use as a medicine. There is clear scientific and medical evidence that cannabis is a harmful drug which can damage people's mental and physical health."

And so those seeking cannabis for medicinal purposes must continue to chase it in the same way as recreational users, through the black market. "I considered asking around to see if people nearby sold any," says June, "but I thought: 'Hang on, I'm an old lady! I shouldn't be meeting strangers on street corners.' "

"The problem with buying off the street," says Orson Boon, from the from the London Cannabis club, "is not only are you funding organised crime, you're probably being ripped off. The cannabis is likely to be low quality and when you're using it for medical problems you want a strain you know will work for you."

However, unlike most drugs, the cultivation of cannabis can be done by almost anyone with a small space and a little spare time. And while it is still illegal to grow cannabis, buying cannabis seeds and growing equipment is not.

Boon works in the medical profession and says his interest in cannabis began after seeing the effect it had in alleviating the pain of a patient with Huntington's disease. He says he now receives hundreds of emails a day from people with problems ranging from MS and epilepsy to depression. Initially, many were looking to it as a last resort, but the recent legalisation of medical cannabis in certain US states has changed this. "People read about what has happened in other parts of the world and want to try it themselves. I've noticed a huge increase in people coming to me knowing exactly what kind of weed they want.

"There is a huge, huge community of cannabis growers and one of the nicest parts of this community are those who give it away for free to medicinal users – they are often referred to as 'caregivers'. In my experience, these people could be anyone, from small-scale to commercial growers."

One hugely influential figure in the development of medicinal cannabis in Britain is Jeff Ditchfield, who in 2002 founded the organisation Bud Buddies, which supplied cannabis to ill and disabled people free of charge. He operated from a cannabis coffee shop in Rhyl, north Wales that, despite being under constant surveillance and subjected to six police raids, became a pivotal part of the local community until 2007, when he was forced to relocate to Spain.

Unlike the UK, the Spanish constitution says that to prosecute a cannabis-growing offence you have to prove it has affected public health and the supply of cannabis in Spain is only illegal if you are profiting in some way. "The law is much more in line with the Bud Buddies philosophy," says Ditchfield, whose interest in the subject began when a close friend with MS complained they were having difficulty obtaining good-quality cannabis. "So I decided to help."

The choice of Spain was also fuelled by the open-minded attitude they have to research in medical cannabis. "In Britain it is near impossible to do any kind of research," says Ditchfield. "The NHS are still at least 10 years away from having cannabinoid cancer treatments widely available. What are people expected to do in the meantime? For me, the choice between being a dead law-abiding citizen or a living cannabis criminal is no choice at all."

Daniel Williams, a spokesman and researcher for Release, the national charity providing expertise on drugs and drugs law, concurs. "There are almost as many suggested medical uses for cannabis as there are cannabinoids, and while considerable research has been done into some of them, this is not a field in which the UK has been a leader. This is at least in part due to the legal status of cannabis in the UK, where it remains a schedule 1 drug under the Misuse of Drugs Regulations 2001 – meaning it is not recognised, in its natural form, to have any medicinal or therapeutic value. In countries such as the US, where medicinal use of herbal cannabis has been permitted in certain states for many years, clinical trials have been conducted that have revealed many therapeutic applications. Unfortunately, the prevailing political and moral attitude to the use of cannabis in its natural form in this country has stifled research on the grounds that the risks, which are rarely well studied in themselves, outweigh any potential benefits."

At Bud Buddies they focus on producing cannabinoids as opposed to cannabis. Cannabinoids, such as CBD and the psychoactive THC, are the chemical compounds within the plant that cause the "high" sought by recreational users. At the moment, Bud Buddies specialise in developing 1:1 oils, which means equal amounts of THC and CBD, as when combined they can be more effective. CBD also moderates the psychoactive effects of THC. This is the basic makeup of the pharmaceutical cannabis-based drug Sativex, which is used to treat MS.

"The most exciting development," says Ditchfield, "is the discovery of the effect of cannabinoids on cancer cells." According to Cancer Research UK, there isn't enough reliable evidence to prove whether cannabinoids can effectively treat cancer. However, research continues all over the world and last week scientists at the University of East Anglia showed that THC could in fact help combat the growth of cancerous cells.

Bud Buddies receives support and sponsorship from companies within the cannabis industry but also raises funding from books and seeds sales. This year, the organisation will open a cannabis dispensary in Puerto Mazarrón.

Ditchfield has lectured about the medicinal properties of cannabis to the Royal College of GPs in London and to final-year pharmacy students at Liverpool John Moores University, and, with Mel Thomas, has written The Medical Cannabis Guidebook: The Definitive Guide to Using and Growing Medical Marijuana, due to be published later this year. Thomas joined forces with Ditchfield after serving a five-year sentence for production of skunk cannabis valued at £2.8m; this "horticultural expert" (as the trial judge called him) now uses his skills to help Ditchfield with the production of medicinal cannabis.

Kem O'Sirus is 35 and from London. He began growing cannabis 12 years ago on a large scale with the sole aim of making money but after encountering a customer with arthritis he started giving it away as well. "I used to see growing as just a way to pay the bills. I was good at it and knew what to do. But having seen first hand the benefits of cannabis for sick people it changed my purposes. I am a medical user myself and take cannabis for depression and anxiety. I believe that cannabis as a medicine and health supplement is incredibly beneficial. I help who I can when I can. I do not charge and I never will. I didn't want a life where I was skulking around with boxes of weed and meeting dodgy people. I've got two kids and I'm the creative director of a business – I don't want to be a criminal. In my brain I feel like I'm doing the right thing." O'Sirus is able to fund this through the cannabis he sells to recreational users. "I can justify the selling this way," he says. "I make money from the recreational users but what they don't know is that they are subsidising the medical users."

O'Sirus makes a lot of his medicines from other growers' leftovers – a part of the harvest known as "trim", the leaves of the plant cut away from the actual flowers. "I'm a firm believer in using the whole plant. The things I've done from other people's rubbish are unbelievable. When you obtain cannabis this way you don't have to charge as 90% of growers will want to get rid of their trim. One man's rubbish is another man's gold."

Cannabis oil is a particularly sought-after product for medicinal users and requires an extra stage of preparation once the plant has been harvested. The demand for oil is so high that many people who sell cannabis on the black market have started producing fake oil, which is often just hemp oil.

Sativex, which is made from cannabis extract, can cost up to £180 and is only available on the NHS in a limited number of areas in Britain. It is rarely prescribed. "Most people who come to me can't afford Sativex. I can make them an oil for less than £10 that will have more or less the same effect," says O'Sirus. "The method I use most regularly is distilling the plant matter in alcohol. You're left with a black oil like a tar that tastes very bitter." He also makes food containing cannabis, to make ingestion easier. "I don't just hand out bags of weed."

O'Sirus has supplied medicinal cannabis to more than 100 people; he has 12 regular customers now with ailments ranging from rheumatism, back pain, RSI and insomnia through to more serious problems such as MS, motor neurone disease, Parkinson's and cancer. "I only help people I'm put in contact with directly. Usually only one degree of separation due to the risk involved. Everyone has to be safe." Most of them, he says, have never smoked a joint in their lives, let alone taken other illegal drugs.

"These are the people I like to help. It's all about changing people's perception of cannabis and its uses.

"I'm not saying cannabis is a magic cure but I can definitely say I have seen first hand that it has alleviated pain. I've had failures and I've had people who haven't responded – it is not for everyone. I had someone who felt really sick and it just didn't agree with them. What I do know is that it is a very complex plant. It would be great to have the resources to carry out proper research – but until it is legalised it is just trial and error."

Names have been changed