If you were to close your eyes and conjure the headquarters of a 50-year campaign to legalise and license psychedelic drugs, you might well see “Brainblood Hall”. A Tudor hunting lodge, surrounded by three concentric moats and formal boxwood topiary, it appears, as you approach along its winding drive on a wintry afternoon, to be ready to whisper all kinds of curious stories. There are plenty from which to choose. The Black Prince used to hunt from a house on this site. Lewis Carroll based the chessboard landscape of Alice Through the Looking-Glass on the watery Oxfordshire moorland that extends in all directions. And Aldous Huxley set his first novel, Crome Yellow, here after visiting for tea with Lady Ottoline Morrell in 1921.

Amanda Feilding, who grew up here and returned to live in the manor after the death of her parents, is the natural heir to all of those associations. She is an eye-bright woman of 76, a spirited talker and an attentive listener, with that ingrained aristocratic habit of passing off wild and whirling eccentricity as mundane routine. For the past half century, she has led an indefatigable – and mostly frustrated – campaign to relax the prohibition on research into psychedelic compounds, particularly LSD. What long seemed a hopeless quest, a one-woman battle against the massed artillery of the “war on drugs”, has recently begun to turn in her favour. Feilding has lately been dubbed the “Queen of Consciousness” by the New Scientist. I have arranged to meet her to talk about the ways in which her half century of lobbying seems finally to be paying off.

It is, appropriately enough, by no means straightforward to find Beckley Park (Feilding nicknamed it Brainblood Hall in the 1960s). The postcode I’ve keyed in to satnav first takes me to an MoD firing range. Directions from the landlady of the local pub lead to a golf club car park. By the time I eventually locate the correct unmarked mile-long track, the low sun is losing its brightness on the red walls of the old lodge, lending it an off-grid glow.

Feilding, who also enjoys the titles the Countess of Wemyss and March, and Lady Neidpath, courtesy of her husband, Jamie Charteris, has converted an outbuilding into the two-storey nerve centre of her lobbying operation. Downstairs, her team of five researchers and interns is at computer screens. Upstairs, in a beamed loft, we sit down to tea and biscuits while she talks me through the latest pile of data and research literature and the little, brightly coloured fMRI scans of the brain – this one on LSD, that one not.

Feilding started her campaign from her kitchen table toward the end of the 1960s. But after a while, she thought: “Well, I can’t try to change global drug policy and carry out scientific research as just me. I have to become a foundation.” She was, she says, “lucky or clever” in getting serious scientists to support her. Albert Hofmann, the Swiss chemist who famously had the first LSD “trip” in 1943 after accidentally dosing himself with the compound he was analysing as a cure for migraine, became a lifelong ally. He was joined on the Beckley Foundation’s advisory board by luminaries including Professor Colin Blakemore, director of the Oxford University Centre for Cognitive Neuroscience, and his counterpart at Cambridge, Professor Trevor Robbins.

In the past few years, since the controls on experimentation with psychedelics have been relaxed, the Beckley Foundation has sponsored research programmes at Imperial College London and elsewhere to explore the effects of LSD on the brain, particularly in treating long-term depression. These studies are part of the science that begins to suggest psychedelics may have a role to play in treating everything from alcohol addiction to Alzheimer’s disease to post-traumatic stress disorder. Significant headlines first resulted from a Beckley-funded study at Johns Hopkins University in 2016, detailing the positive effects of using psilocybin, the active ingredient of magic mushrooms, to combat depression in terminally ill patients.

That study was the starting point for a book-length investigation by the influential New York Times writer Michael Pollan, How to Change Your Mind: The New Science of Psychedelics, which topped the bestseller lists last year. Feilding had been arguing for many of Pollan’s findings all her adult life: “We have been stuck with SSRIs [such as Prozac or Zoloft] as our only tool for treating depression,” she says now, “and meanwhile there has been an epidemic of mental illness.” It is Feilding’s as yet unproved belief that LSD in controlled dosages has the capacity to “get deep down in the brain and reset ‘the wish to get better’ – like shaking up a snow globe”. She began microdosing herself in her 20s. “We used to call it a psychovitamin,” she says. “It makes you more lively, you enjoy your thoughts more. You can find your flow.”

In the years since President Nixon outlawed LSD in the wake of the Charles Manson trials, prohibition codified in the Controlled Substances Act of 1970, it has been virtually impossible for pharmacologists to show an interest in Hofmann’s “wonder drug”. One of the reasons that Feilding has been able to keep the argument going through those years, however, is that she has existed outside the academic establishment. She has no university degree. It would be fair to say, however, that her credibility as an advocate has not always been helped by her storied history with self-experimentation. This reached an infamous extreme in 1970, when Feilding became enthralled by the ancient practice of trepanning, the drilling of a hole in the skull, in the belief that it would expand consciousness and reduce neurosis (a practice that, needless to say, has zero support in the medical profession). Following the example of her former lover and mentor Bart Huges, a Dutch natural scientist with whom she first experimented with LSD, Feilding carefully bored a hole in her own skull using a dentist’s drill.

Amanda Feilding at ‘Brainblood Hall’, her Tudor home and nerve centre of her thinktank, the Beckley Foundation. Photograph: Karen Robinson/The Observer

She made an artful film of the process, designed to be shown to the curious (somewhat gruesome clips from which are discoverable on the internet). The film did not endear her to mainstream science, but that experience was nothing new.

“Funnily enough, growing up here as children, we always were so far out of society,” she says, cheerfully. “My parents had no cash for heating or petrol or toys or school uniform or whatever. I was always very isolated. So becoming a pariah made not much difference to me. And I always had a couple of other pariahs for company.”

That rebellious streak was inherited from her father, whose mother had been a friend of Nietzsche and “all that lot in Europe”. He used to do his hedging and ditching at Beckley at night, by torch and candlelight, because he believed daylight should be reserved for making art – he was a painter who didn’t really sell. Feilding trailed around after him at all hours. He read her Seven Pillars of Wisdom when she was six.

Her mother was potentially less forgiving, an impassioned Catholic who believed that her daughter should live at home until she married. “I have to say, I admired her in old age, though,” Feilding says, with characteristic brightness. “There I was, druggy, trepanned, unmarried, with two sons – bastards, as she might have seen them – and she didn’t mind a bit.”

Before the light outside goes, Feilding insists that we have a wander around the grounds, where the seeds of her curiosity were sown. Out among the ancient hedges and ponds she points out the mound and tree stump that she believed housed a private god figure; her game, aged five or six, was to find ways to make that god laugh, “that kind of orgasm experience that I think a lot of young children have and then forget”.

Feilding did not forget. She wanted afterwards, she says, to recreate that childlike intensity of experience. She discovered pot at 16 and left her convent school when she won the science prize and the nuns refused to present her with her chosen book about Buddhism. She decided to continue her education by going in search of her godfather, a man named Bertie Moore, who had been “a spycatcher in the war” and was by now living as a Buddhist monk in Sri Lanka. Feilding, with £25 in her pocket, got as far as the Syrian border, where she spent some time living (of course she did) with Bedouins before returning to study comparative religion with an Oxford professor and fine art at the Slade school in London.

Her first experience with LSD was nearly her last. An acquaintance spiked some coffee she was drinking with a massive dose and she spent three months recovering from the “psychic wound” in a little hut she points out at the end of the garden. She was eventually persuaded out of the hut to a party at which Ravi Shankar was playing, in London. It was there that she met Huges, who had not long returned from Ibiza, where he had been making his own LSD. Huges was a man after her own seeker’s heart. He had been, she suggests, the top medical student in the Netherlands.

“Then,” she says, “he called his daughter Marijuana, and trepanned himself, and inevitably they failed him in his finals.”

The day after they met, Huges followed her down here and they started their hallucinogenic romance. As Feilding explains this former life, in digressive fits and starts, fretting a little that she is saying too much, she leads me through the twilit garden, over well-trodden stepping stones, pointing out a pond she dug “based on sacred geometries”, with a half-submerged colonnade as if from a forgotten civilisation.

It is hard to separate her from her habitat in the dusk; she says she thinks of the house as her soul. She feared she was going to have to lose it when her parents died. The house went up for sale and Drue Heinz, the baked beans heiress, expressed an interest. Feilding eventually managed to secure it by – she suggests, half-joking – letting her two young sons hide in the woods with air rifles to frighten off prospective buyers and by indulging in some financial smoke and mirrors with the bank.

Her desire to stay was wrapped up with the experiences she had here with Huges. His cultish philosophy, which she imbibed enthusiastically, along with his drugs, was based on the notion that in evolving to stand upright, human beings had lost some of the vital blood volume in their brains. One result, Huges argued, apparently persuasively, was that the ego had come to dominate more vital connections with the external world. The broad hypothesis was that LSD, with its action on blood capillaries, restored that connection, flooding the senses and allowing us to experience the world something like a newborn baby did. The key to controlling those trips, Feilding discovered, remembering the hypoglycaemic collapses of her diabetic father, was to keep sugar levels high in the blood as the drug depleted the body’s energy.

At some point in these experiments, Huges made the mistake of explaining his brain-blood-volume thesis to a journalist. A few nights later, Feilding says, there was a knock at the door of her London flat and two burly gentlemen (“from the Home Office or wherever”) advised Huges that he should return to his native Holland. He was, Feilding says, unable to return to the UK for 25 years.

As she completes this story, Feilding leads me into the main house itself, with its panelled walls and huge stone fireplaces and Ottoman rugs and tapestries. She fetches down a skull from her mantelpiece and shows me its several trepanned holes. The skull, she insists, was recovered from the grave of an Irish chieftain from 700BC; it is the cue for a brief history of skull boring in ancient cultures in Germany, India and Central America. The practice was, she believes – not entirely in step with received anthropological wisdom – most commonly associated with the priesthood, those with access to the best drugs. “The ones with the holes in the head became the shaman.”

And what about her own experience with the dentist’s drill. Did it change her life?

“I wouldn’t go that far,” she says. She recalls in passing a terrible journey home from Amsterdam back in the 1970s, when she had gone to visit Huges and had taken strychnine instead of mescaline and nearly died. When she got to London, Joey Mellon, her fellow traveller with Huges and subsequently the father of her sons, was trying and failing to make a hole in his skull with this “ancient handheld trepan”. Was that a moment, I wonder, when she felt their experiments might have been going too far?

“I took it more as an example of how not to trepan,” she says. “When I did it myself, I was very careful; I had practised for a long time.”

She lost the movie of the operation for a while, but rediscovered it. I wonder how it felt to watch it now?

“Actually, I think it is rather beautiful,” she says. “And terribly English. It starts with the bird, of course, who flies off from the attic window.”

The bird in question was a tame pigeon that Feilding had found as an orphaned squab, fed using a paintbrush, and which subsequently lived with her for 15 years, coming and going from the house as it pleased, sometimes sitting on her shoulder, Long John Silver style. “Birdie” was the reason she did not follow Huges to Holland. “He is,” she says with certainty, “the reason I know telepathy exists. He would look at me before he flew off, as if to say, ‘You poor person, why don’t you fly away with me over the river?’”

She pauses, laughs. “I know that sounds mad, but to my mind it was not mad at all.”

Keen to return to the challenges of the present, Feilding takes me back up to her loft office and her excitement at the current Beckley-sponsored research. When I mention Pollan’s book she expresses dismay that although the New York Times writer visited her here, he did not acknowledge in his book her work in shaping the debate around legalisation. “He wrote me out of it,” she says. “I have learned it is quite easy to write a woman out.”

Her vision and energy have led to transformational changes in international drug policy Sir David Nutt

She leafs through some of the foundation’s reports on her desk.

“When I got involved, global drug policy was in the dark ages,” she says. “I was really just interested in cannabis and the psychedelics and horrified how they were classified in the same bag as all other drugs, heroin and cocaine and the rest.”

Feilding launched a series of seminars through the foundation, Society and Drugs: A Rational Perspective, which drew in speakers and policy-makers from across the world. She leveraged her influence to help frame a more realistic approach by the UN and sympathetic governments toward cannabis in particular. Psychedelics remained more of a taboo subject. Sir David Nutt, another of her Beckley Foundation advisory board, lost his job as chair of the Home Office committee on the misuse of drugs in 2009 for stating that “the drug ecstasy is [statistically] no more dangerous an addiction than horse riding”. He could have gone further, Feilding suggests. “Cannabis and psychedelics are non-addictive. They have been used as medicines since the beginning of human history. I think,” she says, “our meetings were quite influential in persuading important people of that fact.” (Nutt, now chair of the neuropsychopharmacology programme at Imperial, later confirms to me how “Amanda’s remarkable vision and energy have led to transformational changes in both international drug policy and research with psychedelic drugs”.)

A faith in conventional scientific method seems to have partly supplanted some of the more speculative theories that Feilding adopted from Huges. In the years before the latter’s death in 2004, she dismissed some of his later conjecture, she recalls, as “rubbish”.

In London with Joey Mellen (left) and scientist Bart Huges, 1966. Beckley Foundation Photograph: Courtesy Amanda Feilding

I wonder if any of the research she has done with Imperial College has vindicated Huges’s original blood brain notion? She admits it has not. When she helped to lead the first brain imaging study with LSD, the scans did not reveal the increase of blood supply she had been expecting, though they did show a decrease in what she calls the “conditioned reflex mechanism”, the controlling effect of the ego. The principal investigator in the study, Robin Carhart-Harris at Imperial, subsequently suggested that blood flow was probably “a little bit of a sideshow… The brain doesn’t fundamentally work through flowing blood. That’s part of it, but we know that the function is electrical, so why don’t we measure the electrical signals?”

Those signals, on Feilding’s primary-coloured fMRI scans, seemed to illustrate the mechanism that Aldous Huxley more poetically described as the opening of the doors of perception. Feilding points me to the patterns of colour on the brain scans. “The activity in the visual centre on the brain connects with a dozen other centres, so you get this flood of emotion and memory and colouring and music,” she says. “That is what people have been trying to describe.”

When Feilding launched this landmark study at the Royal Society in 2016, she did so in honour of Hofmann, who had always wanted to be welcomed there, but never was. Hofmann remained president of the Beckley Foundation right up until his death, aged 102, in 2008.

Had he died frustrated that his “elixir” had apparently been consigned to scientific history?

“No, Albert was a very happy man,” she says. “He felt this was a gift he had been allowed to give the world. Though the world didn’t seem to want it then, he knew it would at some point. I promised him I would get it re-established and that’s what we are doing.”

The study that she is “zooming in on” is the trial of psychedelics with terminally ill patients. “It clearly brings this contentment to many people,” she says. The original small, double-blind study showed a range of responses, but 80% of those involved showed significant decreases in depressed mood and more than two-thirds announced their experience with psilocybin as one of the top five most meaningful experiences in their lives. Does it matter, does Feilding think, if such experiences are illusory, a pharmacological trick?

“If it makes your dying better, and gives comfort to all those around you, who cares?” she says. “And perhaps it gives us a glimpse that we are more connected to the world outside ourselves than we think.”

Does she retain the faith in a meaningful universe that she felt as a child?

“Well, it is utterly amazing, whatever you call it. And on every scale: billions of stars, billions of neurons. I think it’s reasonable to believe there is some kind of connection between all of it.”

She returns to other favourite strands of research – a collaboration in Brazil using ayahuasca to make neurons fire in a petri dish; her plans to look into the ways psychedelics might encourage “brain plasticity” in Parkinson’s patients; an idea to try to prove enhanced cognitive function by studying the effects of LSD on winning strategies in the board game Go; policy roadmaps for the regulation of cannabis and MDMA.

She punctuates these accounts with occasional expressions of the pressures all this work places on her time. Feilding remains very involved in the lives of her sons: Cosmo, the youngest, is a film-maker, most recently of The Sunshine Makers, a documentary about 60s counter-culture; Rock, five years older, “rebelled” to become deputy leader of Kensington and Chelsea Council, until his abrupt departure after the tragedy of the Grenfell Tower fire, a “terrible, terrible time” that Feilding has no wish to discuss in detail. She has two grandchildren, twin boys aged five. Does she have enough time to spend with them, I wonder, or, rather, does she never think her work is done?

“No,” she says quickly, “I love the work, but then I sometimes think, what am I doing? I love the research but I don’t love the policy.”

Whatever the case, she suggests determinedly, now that she feels she is winning “after 45 years of not winning” she is not going to give up soon. It’s pitch dark outside by now and Feilding walks me out to the car. She is anxious that I concentrate on the work rather than the personal history. I reassure her as far as I can, though it seems to me that you cannot separate one from the other. Then she waves me off, and I watch her in the rear-view mirror disappear back into the shadows of Brainblood Hall and her lifelong mission.