Carly Barton winces when she talks about the pain: “A ridiculous amount of all-over pain – it just feels like you’re burning from the inside out, like my bones have been replaced by red hot pokers.”

Following a stroke at the age of 24, Barton developed the neurological condition fibromyalgia, which meant she was in constant pain. Doctors gave her increasingly strong opiate pain relief, to a point where she was drinking morphine every two hours, as well as wearing a fentanyl patch. She says she was “completely off my face, and still screaming down the house in pain”.

She spent six years pretty much in bed, went down to six stone, couldn’t eat, couldn’t think, couldn’t converse. Before this, she had been teaching art at university, sculpting, welding, running around. Now she “wasn’t really a person, I was just sort of breathing in and out, trying to get to the next lot of painkillers, really”.

She had been worried about trying cannabis for pain relief. Already depressed, she was concerned about how it would affect her mental health. But it got to a point where she would try anything. “Like bloody crystal healing – do you know when you get to that point? That’s the fuck-it point.”

Instead of crystals, she smoked a joint, sitting on her front doorstep, and for the first time in six years she felt no pain. She says: “It was kind of like I’d lost my handbag or something – you know that feeling when you think you’ve lost your phone, something’s missing but you’re not sure what? It was like that. I wasn’t expecting it, thought it might help me sleep, or just be another one of those things that don’t work. I lay completely still because I didn’t want to move, I didn’t want to ruin it.”

The first day of cannabis was the last one of morphine. She also weaned herself slowly off her other prescription drugs. “You feel like a heroin addict,” she says. “It was like Trainspotting, but more boring.”

Now, she takes cannabis every day, roughly every two hours, using a vaporiser. Is she not just very stoned, all day long? “I was a lot more off my face on pharmaceuticals. I’ve taken a significant amount this morning, to get out of bed, but hopefully I don’t appear stoned.”

She doesn’t. We’re drinking tea in the garden of the Brighton house she shares with her wife and two dogs, Kevin and Oxie, rescued from Greece and Eastbourne respectively. Now 32, Barton walks with a stick, otherwise you wouldn’t know there was anything wrong with her. She is alert, engaged and engaging, incredibly well informed (she admits that activism over medicinal cannabis has pretty much taken over her life – but at least she has one now).

A few of Barton’s fledgling plants. Photograph: Sarah Lee/The Guardian

She followed advice from people in the United States and Canada about building up tolerance slowly, and about which strains of cannabis to use: those lower in THC, the psychoactive constituent of cannabis, but higher in cannabidiol, which has undergone preliminary clinical research, including studies on its effect on anxiety, cognition, movement disorders and pain.

At the moment, her cannabis comes from dealers, but it is not always possible to get what she wants. So Barton has started to grow her own. She shows me her garage, where, in a silver, boxy tent with a light and an extractor fan (all bought for about £80 online), six small plants of varieties she has found beneficial are between a week and two weeks into a journey that will last three to four months until they are harvested. She bought the seeds legally (they can be, for ornamental use), but everything else she is doing is illegal. Carly Barton is a criminal.

Last November, it became legal in the UK for doctors to prescribe cannabis-based medicine. This came after the high-profile cases of young epilepsy sufferers Alfie Dingley and Billy Caldwell, whose symptoms appeared to be helped by cannabis oil. But the reality is that, under hazy guidelines and with a lack of clinical testing, it is still very hard for people such as Barton to get an NHS prescription.

She decided to go private, with a view to converting to the NHS after a month or two, if it could be shown to be working. She got a private prescription from a pain specialist, Dr David McDowell, in Manchester. But then there were permits and licences, in order to import her medicinal cannabis from Holland. In total, a month’s worth of cannabis cost Barton about £1,400; there was no way she could afford to continue. On the street, the same amount of cannabis would have cost a tiny fraction of that. But the prescription felt good. “I didn’t have to look over my shoulder; it felt like I was a legitimate patient. That month was brilliant.”

Alfie Dingley, whose mother Hannah Deacon appealed for a licence so his epilepsy can be treated with cannabis oil. Photograph: Stefan Rousseau/PA

Then, after a two-hour consultation with another pain specialist, Dr Rubina Ahmad, at Haywards Heath hospital, Barton got her NHS cannabis prescription, the first ever in this country. Great news, but that wasn’t the end of it. It still had to get past two meetings of the hospital board, which it just about did. Then it needed to be rubber-stamped by someone from the local authority. It went to Barton’s local clinical commissioning group, who rejected it unanimously, on the grounds that cannabis is an untested medicine.

Barton would like to see the clinical trials for cannabis rethought. “They take three years per condition. Cannabis can treat over 300 conditions, so that’s over 900 years of trials,” she says. “We’ve never been in this situation before, trying to squeeze medicine that has been used for thousands of years into a box designed for brand-new medicines. Rather than sitting around saying this isn’t the way we do things, we need to think how we can do this.”

Whether you agree or not as to cannabis being considered a medicine, it is clearly ridiculous that something can become legitimate only if you pay a lot of money privately for it. “The wealthy are patients right now, everybody else is still criminal,” says Barton, who could afford to be a patient only for a month, before becoming a criminal again. She doesn’t like being one: the association with dealers, organised crime, county lines, stabbings, plus the threat that one night the police might come and kick the door down. She keeps capsules of the cannabis oil she makes by her bed, to take with her if they do come and take her away.

Charlotte Caldwell with her son Billy. Photograph: Yui Mok/PA

When she got her home-growing kit two days after her NHS prescription was blocked, she went to her local police station to tell them what she was doing. “I handed them a signed piece of paper disclosing exactly the location, what strains and weights I had been prescribed, committing to grow only those strains, and anything I grow above and beyond that I will personally come and hand in for amnesty.”

What was their reaction? She laughs. “They literally did not know what to do. The sergeant on the desk said she really didn’t know what to do. She did reassure me that they weren’t going to come and kick the door down, though she couldn’t promise that they never would.”

In response, Barton is setting up Carly’s Amnesty. It is a scheme by which people like her who grow and use cannabis for medicinal purposes, have diagnoses and cannot afford private prescriptions, would declare and register to their local authorities what, where and how much they are growing, and agree to hand in anything above their needs, in return for immunity from arrest and prosecution.

If that sounds more like Utopia than Sussex, she has a meeting with the area’s police and crime commissioner later in the week, to talk about how it might work. She would like to run a pilot in the area, “then we’re going to invite other forces to join, and we’ll take over the UK slowly, in bite-sized chunks. I want this pilot taken seriously. It’s the very least that can be done – to tell people they aren’t going to kick your door down in the middle of the night, or have you worried about your family and social services involvement, because you’re consuming a plant to keep yourself well.”

Barton certainly doesn’t want to go back to how she was. Nothing is cured, she knows that, and she can – and still does – go into spasm. She shows me on her laptop a video of her, apparently locking up, in an unnatural position, her shoulder twisted. These dystonic storms used to happen roughly twice a week, and still do. The difference is how they affect her life now. “That would have been an ambulance job. A&E, anti-spasmodic injections, gas and air for a couple of hours until the injections kicked in, probably admitted, a few days of recovery, then physio. Now, I can bring that down with cannabis. Two and a half minutes on the vaporiser and I can just crack on, do a bit of cleaning.”

Carly Barton is talking at the Women, CBD & Medical Cannabis Conference in London on 18 May. https://3cmconference.com/