In sleepy Sussex is a group of dedicated cryonicists who believe they hold the secret to eternal life. Simon Hattenstone joins them for a demonstration – but first they need to make sure the hosepipe isn't too leaky

In a bungalow in Peacehaven, by the east Sussex seaside, a 72-year-old man and his 62-year-old wife are planning their future. There's no discussion of anything morbid, like death, because, as far as they are concerned there is no such thing as death. When they stop breathing, they will pass into a state of suspended animation. They will be frozen in a giant flask of liquid nitrogen at almost -200C, which will preserve their brains and organs in as fresh a state as possible until technology has advanced to the stage where they can be revived.

Many cryonicists choose to have only their heads frozen – because that contains all the vital matter – and by the time people can be brought back to life it will be easier, and preferable for some, to attach a new body. But Alan and Sylvia Sinclair will have their whole bodies frozen.

For Alan, who used to run a rest home for the elderly with Sylvia, it all started with the death of Queen Mary in 1953. "I was aware from a very young age that life is very short. It occurred to me that no matter what you've got, you're still going to die. I remember thinking, 'I enjoy things: why does anybody want to die?' " He looks at me. "Do you?"

Has he never thought there comes a right time to go? "No, I'm always too busy. In the rest home there were people who were quite happy to go to sleep and not wake up. I couldn't understand that." Some 30 years later, when he was 45, he watched a Miriam Stoppard TV programme on cryonics and within days he had joined up.

Sylvia says everybody thinks she just followed suit, but no. "I thought about it for another couple of weeks before I made my mind up."

Alan now runs Cryonics UK, and every month he holds meetings with fellow cryonicists and potential converts to discuss the practicalities and potential problems of their suspension – of which there are many. First, upon so-called "death", a team of experts must rush to their sides, pump out their blood and fill them with antifreeze. This is complicated because virtually all the members of Alan's suspension team at Cryonics UK have practised only on dummies, rather than real people – and if, for example, air bubbles enter the pumping system, the brain will be irreversibly damaged. Second, there are no storage facilities in Britain, so patients will have to be transferred to the US or Russia. Third, science has some way to go before we can bring people back to life.

But Alan has always been an optimist. He knows the situation is far from perfect, but he is doing his bit for eternal happiness. Parked outside the bungalow is an old ambulance, customised with suspension equipment. It's surprisingly archaic – basically a suitcase with a load of tubing inside, reminiscent of an old-fashioned wine-making kit. Alan credits himself with devising the slogan, "Ambulance to the future."

In the lounge, a dozen people are listening to Alan run through the weekend's agenda. Alan is the oldest; Dave, at 24, is the youngest. His girlfriend, who is only 20, cannot be here. "She was going to join us from the Wirral, but ironically a death in the family has stopped her," he says, sounding remarkably chipper about the setback.

There is jukebox in room, though Alan and Sylvia have yet to buy records to play on it, and scattered around the room are clocks of all ages and designs, each telling a different time. Most of the people wear a silver bracelet, saying they are paid-up cryonicists and that when they stop breathing they expect to be frozen in the agreed manner. Some also wear tags around their necks.

Alan, who looks much younger than his 72 years, speaks in a meandering monotone, while Sylvia makes tea. "Sylvia is going to put arsenic in our tea." It's an ongoing joke, and one that gets to the nub of their problem. The cryonicists are not dying quickly enough, so the opportunity to hone their skills is limited. Alan says he once carried out a suspension, but he doesn't look back at it with pride – it didn't go as smoothly as it might have.

Another man in the room, an ageing hippy called Tim with a thinning ponytail and a philosophical bent, says he has carried out three suspensions – one, in Britain, just involved shipping the body to America, while in the US he was part of a team that performed the cryonics Full Monty, from collection to pumping, decapitation and storage. The others have no on-the-job experience. Danielle, a middle-aged woman from Wales, says she can't stay the whole weekend because she's due back home tonight to sing in Aberystwyth. She's not quite a professional, but is proud of her voice. "That's why I want the full-body thing, cos I don't think I'll get a larynx as good as this."

It was Benjamin Franklin who first suggested, in 1773, that it might be possible to preserve human life in a suspended state for centuries. And that was that for close on 200 years, until physics lecturer Robert Ettinger published The Prospect Of Immortality in 1962, in which he argued that, since we keep food fresh by freezing it, we can do the same with the human body until such time as we have discovered how to defeat death.

The term "cryonics", derived from the Greek kryos, meaning cold, was coined in 1965 when Karl Werner founded the Cryonics Society of New York, and the premise is that memory, personality and identity are stored in cellular structures, principally in the brain. So, if you can preserve the brain in decent nick, technology permitting, you can eventually restore people with their personalities intact. The cost varies from $28,000 for head-only preservation to $155,000 for full body.

The largest cryonics organisation, with more than 800 members waiting to be preserved, is the US company Alcor. It was established in 1972 and has frozen 87 patients. The Cryonics Institute, also American, and founded by Ettinger in 1976, has frozen 95. The two groups are rivals. When men walked on the moon at the end of the 60s, eternity did not seem such a huge leap for mankind. But progress has not quite kept up with our dreams.

Back in Peacehaven, Tim asks Alan how he has been. "Fine," he says. Then he pauses and says that's not quite true. "Well, not so fine, actually. I almost went the other day. My heart rate went up to 230 – I thought that was it. I was exercising, just walking on the machine, and it went..." He says this with a peculiar mix of panic and excitement.

US cryonics guru Mike Darwin. Photograph: Murray Ballard

The plan for this weekend is to make a cool-down box for the newly (temporarily) deceased. Alan can get impatient with members who say it's all too complicated, and there's too much to remember. In the end, he says, it's just a basic plumbing process – out with the blood, in with the antifreeze. "I don't mean to be rude, but I try everything out on Sylvia, and if she can do it, ­ anybody can." Fortunately, Sylvia is in the kitchen making another cup of tea.

Even more important than the ice box is this weekend's star guest, Mike Darwin. He is yet to arrive, and Alan briefs the gathered few with a mixture of awe and dread. Darwin was born Michael Federowicz in Indianapolis, Indiana. He worked as a dialysis technician and adopted the name Darwin for his cryonics persona. At the age of 17, he carried out his first suspension for the Cryonics Society of New York at the request of Saul Kent, another significant figure in the cryonics world. In the 80s he went on to become president of Alcor, but was dismissed in controversial circumstances. Sinclair says Darwin is probably the world's leading cryonics authority. But the news is not all good. "He's well worth listening to unless he's in a depressive state – then it all becomes a bit pointless."

A few minutes later a man enters the room. He bears a disarming resemblance to the infamous prisoner Charles Bronson – shaved head, beard, sweat pouring off him, muscular, starey eyes. It can only be Darwin.

Alan tells him he didn't recognise him. "That's because I've lost 56 pounds since you last saw me," Darwin says. He sits down. It's a hot day, and his shirt is soaking. Within minutes he is arguing with Sinclair and his followers, making it emphatically clear that he is unimpressed with their Dad's Army approach to eternity.

Darwin has spent decades suspending dogs, rabbits and humans, and he can't see how such an inexperienced, higgledy-piggledy group can hope to succeed. "The approach has to be widespread, aggressive. We have to be as rich and as big as Scientology. We must have that level of commitment." He stops. "Maybe that's not the best example."

The thing is, he says, he knows the demand is there, if they can only get the technology right. He tells a story about post-Soviet Russia, where he is working with a new cryonics group, KrioRus. As he does so the sweat pours through his shirt until it is the dry patches that stand out. "Eighteen years ago, you wake up and there's no health service, no social security, no scouts, no government, no benefits, no retirement benefit and no God. The whole belief system goes – that's what happened in Russia. And yet people were asked, 'Would you want to live for ever?', and 20% of the population say yes, they want to live for ever, under any conditions." His eyes get bluer and bluer until they turn green. Darwin does not simply proselytise for cryonics, he proselytises for cryonics as big business.

But, he says, you're not going to get anywhere until you start giving it the time and expertise it needs. "In America, we didn't do it until we started regular animal experiments. You need to establish a teaching and training environment. Read the book The Knife Man, about John Hunter, one of the greatest men in your country. The greatest surgeon in London, and they wouldn't even let him lecture in the official facilities. He had to build his own building in his home to teach his students." Darwin feels he has much in common with Hunter, a prophet without honour. "He created disciples, students who went all over the world and took what he taught them. That's what we were trying to do; establish an environment to create a self-perpetuating professionalism."

"That's what we're trying to create," Alan protests.

"No," Darwin says. "No, no you didn't and you couldn't for several reasons. One, you couldn't do the animal experiments – the culture here prohibits it. I'm sorry to highlight disagreements, but this is where we are at. The key to a stable cryonics organisation is to store patients. The instant you do that, people take you serious, because you have taken on the commitment to care for people for a long, long time. The men from the boys are quickly separated at that point. Two-thirds of the people who were on my suspension team in the 70s and 80s are now on liquid nitrogen – people I laughed with, had dinner with, shared personal animosity with, shared great triumphs with, shared personal friendships with. That is what really holds the group together, and it becomes a tangible place that people can show and go to."

"I always intended to do storage," Alan says, "but I thought I was too old."

Darwin gets a "gotcha" glint in his eye. "Alan, you've just given the reason why it didn't happen. You were the principal person people looked to here for leadership, and when you said, 'I don't want to be stored here', that was a no-confidence buster for everybody else."

Silence.

Darwin: "I want to advance my field – cryonics."

Alan: "So do we all, but we can't work full-time on it."

Darwin: "With no experience, you will fuck that patient up. Every time. Not just once. Every time. Get training and practise." That, Darwin says, is the key to progress. "The teaching environment was wrecked by Jerry's arrest, then they got rid of me, and then they got rid of everyone systematically." Nobody blinks when he mentions the arrest.

Alan: "What practice can we do?"

Darwin sets them a challenge: "Do a really honest demonstration, with pre-set goals, and see how many mistakes you make."

The cryonicists break for lunch. The morning session has been heavier than even Sinclair expected. Sylvia has ordered in fish and chips for everybody. A good bit of stodge restores calm.

I ask Sinclair about the arrest that Darwin had mentioned. "Ah that," he says. It's an old story. Jerry Leaf, a cardiothoracic surgery researcher, was vice-president of Alcor and Darwin's partner. Between them they invented a blood substitute capable of sustaining life in dogs for four hours at near-freezing temperatures. "Jerry's arrest... totally bloody ridiculous. He had suspended a woman. She was 97 years of age, she had senility, they moved her from the nursing home to the facility and she died there. Anyway, the police came in and tried to arrest them all for trying to hide her. There was a great big court case."

What was reported as "the strange case of the frozen head" in the Los Angeles Times occurred in 1987, following the death of Dora Kent, the mother of Alcor benefactor Saul Kent. Dora Kent, who was actually 83, was moved from a convalescent home to Alcor by her son. Alcor officials told police she had died a natural death and only then was her head surgically removed by Leaf.

After Alcor applied for a permit to cremate Kent's headless body, the Riverside County coroner's office launched an investigation, noting that she was not under a doctor's care at the time of her death. Investigators sought the right to defrost and examine Kent's head, but a Superior Court judge ruled that this would be an unconstitutional infringement on a person's right to choose how to dispose of his or her remains. The coroner, Raymond Carillo, ruled that tests on Kent's body tissues revealed her death was a homicide, resulting from a lethal dose of a barbiturate. Alcor officials admitted that she had been given the drug Nembutal, but insisted it was used after her death to help preserve brain cells.

Leaf was arrested, but in 1990, after three years, the investigation was closed due to lack of evidence. When Alcor was cleared, Darwin told the Los Angeles Times: "This was a terrible injustice and it has meant three years of fear and anxiety for us. Any time you are accused of grand theft, homicide and other untruths, it is damaging to you both personally and professionally." A year later, Leaf died following a heart attack and was cryonically suspended by the Alcor team led by Darwin. In 1992, Darwin left Alcor for undisclosed reasons. Today, he is a freelance cryonicist working with the Russian organisation KrioRus.

Mark, Tim and David are sitting at a table eating their fish and chips. All wear their bracelets and are fully paid-up cryonicists – though it emerges that they are paying very different prices. David pays £6 a month for life insurance, and he will be suspended by the Cryonics Institute, a not-for-profit organisation located in Michigan, US.

Mark looks flabbergasted. "I'm curious to why you're only paying £6 a month. Mine's a lot more than that." He looks at him, and suddenly he understands. "Oh, you're quite young. I'm 45."

They are still recovering from Darwin's assault on their amateurishness. All three think he was too negative. "It made me angry that someone significant in cryonics was prepared to sit there and say, 'You can't do it because that's not what cryonics people do,'" Tim says. "They say we'll have to make it work. It didn't make sense to me."

"It's not just negativity, it's perfectionism," Mark says. "But perfect is never achieved."

We talk about the type of people who are attracted to cryonics. All three agree they are likely to be men, often with an interest in science and an underlying optimism. Mark, a software engineer, says, "There are quite a few software or IT people involved. Software engineers tend to think too much and go outside the normal boundaries of the general population because they spend all their time abstracting about things."

Why do they want to live for ever?

Tim says the first time he thought about it was when he heard that Walt Disney had been frozen. It turned out not to be true, but he couldn't get the thought out of his head. "It started when I was six and I realised it was a rubbish idea to be dead. I was frightened of death. Basically, I started to think of ways to solve it."

"It's not fear in my case," Mark says. "I was interested as a kid in time travel and time travel is technically not possible, so this is the best solution."

David, a care officer for adults with physical and mental disabilities, says dying is for the defeatist. "I realised that if I lost my life, I'd lose everything I'd ever achieved, loved, enjoyed. It would be as if I never lived, because from the cessation of life there is nothing more."

How would they like the world to have changed when they return? "It would be nice to come back and have a proper democracy," Mark says.

David's having none of that liberal nonsense. "My opinion is, there's been no real democracy since the Greek city state of Athens, and if there were real democracy there would be a problem because mob rule isn't the way forward. We're living on a planet with six billion suicidal maniacs. Do I really want to trust everything to their vote?" The six billion maniacs to whom he is referring are the world's non-cryonicists, who have accepted death as an inevitability.

Mark: "You sound a bit paranoid to me."

David: "I am paranoid – about my personal security. I'm the kind of person who will tend to listen to exit instructions on a plane. When I'm sat in a room, I don't sit with my back to the door..."

Why? "Because I want to keep myself alive at all costs."

I ask if they have read Gulliver's Travels, the novel in which Jonathan Swift imagines a group of immortals called Struldbrugs, who continue to age and are hated by the rest of the population because they are so ugly, useless and parasitical. What if life were like that for them when they came back? David says that's not even worth considering. "If geneticists like Aubrey de Grey get their way, ageing won't be an issue. But even if it were an issue, personally I'd rather be ugly and hated than dead."

Most of David's nearest and dearest are cryonicists and that creates a special bond. "I think it's more of a meaningful long-term relationship dynamic if somebody's planning to live for ever than die in a few short decades. I'm more into that kind of relationship."

Ultimately, it's a sense of duty that drives him on towards immortality. "Cryonics is a potentially life-saving medical treatment, so to not get cryonics is to have passive euthanasia and I'm not suicidal."

Tim says a strange thing happened to him recently – he suffered a crisis of cryonics conscience. "I knew it was going to happen and I was a bit annoyed when it did. But once you have a family you think, 'I'm supposed to die. That's the way it works.' When you're a single person you're self-obsessed, you want to live for ever, and that's as simple as it is. I had a daughter and I did think, 'This is all wrong, I am actually supposed to die, it's just an inevitable process and I need to pull myself together', and I nearly packed up."

Why didn't he? "That's a good question."

The cryonicists screw up their fish and chip paper, put it in the bin and head to the laboratory – which is nothing more than Alan's back room with a table and a case sat on it. Tim's put any doubts to the back of his mind. He's raring to go. "There's a patient on the table dying. Hurry up."

But, of course, the patient is imaginary. Tim takes the lead, explaining the ins and outs of the tubing to his less experienced fellow travellers. Meanwhile Mike Darwin watches, arms crossed reprovingly, his concern for the patient growing by the second.

"Right, I started timing you three minutes ago," he says.

A good few minutes later Tim and his not-so-crack team are still working out where the red and blue bits plug into. "The only thing that goes wrong is if you switch it on without all the bits plugged in. It doesn't like it and it has been known to go bang," he says cheerily.

Darwin can't contain himself. "If I had that kit here, I'd be scared shitless. Shitless. There are some critical things wrong with the setup of that circuit." He tells the team they have made so many mistakes the patient would have suffered irreversible brain damage by now. Darwin suggests technology has regressed since he was in his cryonic prime 20 years ago.

But the water is pumping through the system, and Sinclair's team are fully focused on saving their imaginary patient. Whatever Darwin tells them, they believe they are ahead of their time, not behind it.

"One of the theories I hear bandied around is that the people who are involved now are a bit weird," Tim says. "We're the kind of people who would have bought the laser discs before they became mainstream, with the old Laserdisc player. Apparently, it's called being an early adopter. The people who think it's weird are just too frightened to put the effort in."

David nods in furious agreement, and repeats his mantra. "We're living on a planet with six billion suicidal maniacs."