When I first saw homeless people begging on the street as a child, I couldn't understand why everyone was walking past instead of helping them. By the time I'd moved into my own place I'd developed a more cynical understanding of the world. But still, as I looked over the red light district where I lived, I was frustrated that there seemed to be nothing I could do but watch as flat-chested, underage girls, looking like they were playing dressing-up in their mum's clothes, were picked up by a string of men. My flatmates were also shocked at first, but we got used to it after a while.

Perhaps it is human nature to ignore what is difficult to process. People seem to become invisible to most of the world once they've taken a path which leads them too far out of the mainstream. Once outside of everyday, acceptable society, people function in their own underworld. They can pass under the radar and live in circumstances we like to think we'd never let our friend or neighbour cope with alone.

And once you're outside it can be hard to get back in. If you've led a pretty average life so far you can expect someone to intervene if you find yourself with maggots in your legs, or you lose your memory, or if people sell you for sex or keep your children from you. If you've not come from the safety of a conventional lifestyle you may find it far easier to slip through the net.

I have spoken to five people who have found themselves on the outside to see how it has affected them. Most of the people I spoke to during my research were ultimately helped by charitable organisations. Most of these organisations have recently lost funding and have already stopped their work or soon will do. It remains to be seen what will happen to people who find themselves in similar circumstances in the future.

Natasha Morgan (not her real name), became involved in drugs and prostitution

By the time Natasha failed rehab for the fourth time at the age of 18, her criminal convictions were adding up. She was scared of stealing to fund her habit and going back into prison again. A girl she knew took her to see a man who would "help". Before she knew it she had prostituted herself. "When I thought about what I'd done I was so horrified that I felt I needed to get out of my face to block it out – which meant I had to do it again to pay for the drugs. I got stuck in a distorted cycle."

Today, 10 years on, Natasha is an intelligent, thoughtful mother of two children with a good partner and her own successful business. She does youth work and volunteers for her church. She says: "The more I heal, the more healthy choices I make".

Yet the lifestyle that she leads now could actually be considered more surprising than her past. Her upbringing is more typical of those who end up in prostitution. Home Office figures show that up to 70% of prostitutes have spent time in care; 45% report sexual abuse and 85% physical abuse within their families. It is testament to Natasha's strength of character that she has come out the other side.

Her father was an alcoholic who left their home near London when Natasha was 18 months old. Her mother brought her up as best she could, but she herself had come from a dysfunctional background and didn't really know how to parent. Her mother remarried but Natasha's stepfather came to reject Natasha once he had his own children and was sometimes aggressive. She occasionally saw her father, but he would leave her at her grandmother's where she was sexually abused by another family member.

Eventually her stepfather left and her mother had a breakdown. Natasha says she did not know how to deal with the emotional turmoil and started self-harming aged 11, but this only caused her to become further alienated from her family.

She started to leave herself open for more abuse. "Because my sexual boundaries were confused from a young age I became promiscuous, because a part of me thought you got attention and love through sex. The more that happened, the more rubbish I felt about myself.

"I got on to drugs when I was about 12 years old so I could escape reality, but the more I tried to escape, the more consequences there were for my actions."

At 14 she ran away from home and was raped, became pregnant and had a termination. "It all really battered my self-esteem and I got more into drugs to block it out. I had no one and I just went from one abusive relationship to another."

She says the worse she felt about herself, the worse she allowed herself to be treated. It became a self-fulfilling prophecy. "I was in an abusive and destructive cycle and the more you degrade yourself, the more you want to avoid it."

It was during a prison stint that Nathasha's life began to change. "I had enough of a break from that world to see what had happened to me. But I still didn't have the tools to deal with it."

Outreach charity workers encouraged her to change her life. "They told me I was worth something. I'd got to the point where I thought, 'This is your life now. Accept it. This is how it's meant to be,' but they showed me love without wanting anything back. Apart from them I had no interaction with normal people in society. I lived in a hazy bubble and that became my whole reality."

She says all the women she met involved in prostitution were stuck in the same kind of addictive cycle, whether it be drugs, alcohol or money they needed to make them feel better for the life they lived.

"Maybe 1% of women feel OK about doing it but 99% have very low self-worth, and once you're caught up in prostitution it's so difficult to get out. I think most prostitutes have been sexually abused or experienced some dysfunction in earlier life, and feel so devalued and forget that their sexuality is something to cherish. Their sexual boundaries become so confused and this is open to abuse."

She speaks of the manipulative and coercive pressure from people ready to use vulnerable girls with low self-esteem. One man she worked for gave her a room in his house but controlled her until she was completely reliant on him. Having put himself in a position of power, he then rented her out to other men. It was only when he sent her abroad with a client and she was forced to come off the drugs that she could see clearly what she had to do. On the way home she called a friend to meet her at the airport and escaped.

Natasha followed a 12-step programme and left both the drugs and the prostitution behind. She became a Christian and changed her view of who she was.

Since she got out of prostitution, she has done voluntary work offering support to sex workers and aiming to keep young people out of it. She thinks that if there had been intervention when she was younger and people had helped her deal with her emotions then she would not have ended up as a sex worker. She does not know how the age-old problem of prostitution can be solved, but she sees some of the issues that contribute to it.

"The police once told me going into a brothel is like opening a can of worms. They don't have the resources to deal with it so they basically turn a blind eye unless they see direct evidence of trafficking."

She adds: "It's a massively sad state of affairs that they don't have the money to respond to such a terrible problem. Targeting the buyers might be a better place to start. It's a minefield though."

Natasha has herself done research indicating that there are around 80 brothels in the southern town where she now lives. She says there are a lot of stag parties that use them and there is a perception that it's just a fun thing to do.

She thinks public opinion also adds to the problem: "There is a huge amount of stigma and ignorance around prostitution." She still sometimes feels terrible shame and remorse for the choices she has made. I wonder if perhaps this would not be so if prostitution was seen more as terrible abuse than as any kind of willingly made life choice?

Natasha thinks so: "People actually seem to think that women enjoy it. Who would enjoy that? I don't think anyone from a stable, functional background would end up in prostitution. You can't tell me there's a single person in this world who says, 'When I grow up I want to sell myself.'"

Don Coging became homeless and suffers from short-term memory loss

In October 2011, 67-year-old Don found himself back home in England for the first time in decades. He had nothing but the clothes on his back, his passport and his medical card. Don had been living between India and Germany, where he was working as a gardener, and had no plans to return to the UK.

He thinks his problems really began one fateful night in India. "I got very drunk one evening. I slipped over and banged my head and needed stitches. I ended up accidentally setting fire to my bed and there was lots of running about and shouting. The next thing I know I was being put on a plane to England with nothing but what was in my pockets."

Whether it is from the bang to the head or his drinking no one knows, but Don now has regular short-term memory loss. When he arrived in the UK he was very confused. The authorities brought Don to Nottingham, the last address recorded on his medical card. He was looked after by Nottinghamshire County Council for the night but they said they didn't have the provision for him beyond that. No one else seemed to want to claim responsibility for him.

Ian Nesbitt from the housing support charity HLG, who ended up helping Don, explains: "He was taken to one authority and there were no services for him but there were problems transferring him from one council to another. It was such a tangle. He didn't have a national insurance number as he had been out of the country for so long.

"He had no short-term memory but seemed to respond lucidly when you talked to him in normal conversation, so doctors were saying he was OK."

Sue Hopwell from Ascot House, the residential care home where Don now lives, says: "No one could decide who was responsible for Don's long-term care and who was going to fund him." In the meantime he was left with nothing, confused, knowing no one and fending for himself on the streets.

Outreach workers found him and told him about a day centre he could visit and church-run winter shelters where he could sleep at night. But because of his memory problems, he kept forgetting how to get to the shelter and would end up sleeping on the street in freezing temperatures. On other occasions, he would find the shelter but it would be full so he would sleep outside in the leaves where he said he was sometimes urinated on. "Oh … that place!" is how he sums up his time there.

He says: "When you're on the outside of life it's difficult for anyone to be concerned or to believe your situation. People look through me because I'm too tired or too old or whatever. A lot of people don't treat you like a person, but when I was on the streets other homeless people were good to me because they were in the same boat."

Don's support has now finally been sorted out. When I ask Don how he feels about his situation, he looks a little lost and says: "I don't like being a kept man. A lot of people would but I like to look after myself. I always have." He has lost a lot of his independence and while he's very appreciative of all that the home does for him, he says his situation means he can no longer always choose when to shower or watch TV or lie down without being disturbed.

He explains how it feels: "Everything just seems to be happening around me."

Clara Chifamba is an asylum seeker whose children are still in Zimbabwe

Clara had to flee Zimbabwe in fear of her life after her husband was arrested and murdered because of his political affiliation to the Movement for Democratic Change (MDC), the party set up in opposition to Robert Mugabe's Zanu-PF. She says: "I had to leave for my own safety and the safety of my children."

Clara left her children in the care of her parents so she could secure things in the UK before they came to join her. When she arrived in Luton in 2002, Zimbabwean nationals were free to travel to the UK without a visa because of Zimbabwe's past as a former British colony. She did not know that days after her arrival there would be a change in the UK law, announced in response to the influx of Zimbabweans fleeing political upheaval. From November 2002 Zimbabweans would need a visa to travel in the UK, making it more difficult for them to apply for asylum.

"It was a change overnight and all of a sudden I realised that I couldn't get my family over," says Clara. "I was heartbroken. I didn't know what to do. I just kept saying, 'God, give me strength and energy.'"

Clara is a calm, dignified and self-possessed woman. She tries to keep positive: "I was worried people would come for my parents and kids like they came for my husband but then I told myself, 'No, they'll see you're not there and leave them alone. They'll leave them alone because they're old people and they're children.'"

After the visa rule changes she clung to hope. She was told that it was just a temporary political situation and that it would all settle down, but circumstances in Zimbabwe kept deteriorating. The country was suspended from the Commonwealth due to farm seizures and election tampering. The following year, Zimbabwean officials voluntarily terminated its Commonwealth membership.

Clara says she cannot return to Zimbabwe as her life is still at risk. Returning would endanger her children too, but she feels lost without them. Clara worries about how much they are struggling since her father died two years ago. "He was supporting them. My mum is too old to work and the children have had to drop out of school to work."

In 2007 she applied for asylum, but her solicitor's company went bankrupt shortly before she was due to go to court. She was referred to a new barrister, but Clara says he did not prepare her case properly and she stood no chance.

"My representative turned up late and without sufficient documentation. Even the judge wasn't happy with him. When the judge shook his head and said to the barrister, 'You are not ready for your client!' I knew things had gone wrong. I can't blame the judge; there wasn't much he could do."

Clara was evicted from her accommodation in Bolton with no way to get money. She is appealing the decision, but in the meantime she is not allowed to work. She is currently supported by friends, the church and a small charity, Assist, who help to provide her with a shelter, food vouchers and social support.

"Assist is part of my family now. I'm at peace. Without them I'd be moving from shelter to shelter every night, getting a bed when I could." This is the best she can hope for right now. She is not allowed to function in mainstream society. She has health issues but struggles to qualify for the operation she needs, and without being allowed to support herself there is not much she can do.

"I would like to be like anyone else. I'd love to be able to work and contribute, to sustain myself and integrate more. I'm capable – I wouldn't want to go on benefits." But she adds: "If you come to a foreign country then you must respect its laws and have patience with the system … you can't give up."

Raymond Clayton lives with mental health issues

Raymond, 71, was found by police wandering the street in a confused state and with maggots in one of his legs. He was taken to hospital and it was discovered that he was living among piles of rubbish in his house. He was taken into care for two months while he recovered.

Gina Brumby from Age UK Sheffield's housing support service took up Raymond's case, and has been working to support him ever since. She worries that Raymond and people like him often have to reach crisis point before they are helped: "By the time environmental services got to him his lifestyle had already gone down the pan. I'm all for people living independently but it would be good if there was more of a safety net for people like Raymond. He could have died in that flat."

Raymond had been seen by various services before and had been found living in squalor in the past, but all the services he once accessed ended because he was seen to be in a manageable state.

Gina says: "Perhaps if statutory services had physically gone and done a review earlier they could have saved him. The problem is everyone has such high caseloads, but if he'd been seen perhaps he could have maintained his ability to live independently. Then services would have saved money because they wouldn't be having to support him now."

Raymond's situation had got so bad that he had to pay environmental services to go in and clear the place, which meant disposing of lots of his old possessions. Raymond says he's glad they came: "I don't want to go back to that lifestyle," he says. But it was sudden for him. "That could kill someone – the shock of it all," he says.

I wonder how he got to such a state. Raymond is very intelligent and knowledgeable and certainly physically able to look after himself. But he finds it very difficult to focus on a conversation, constantly going off on fact-filled tangents about anything from the Mersey tunnel to space exploration. He writes everything down, buys things in multiples of two and has a phenomenal memory. He is a fantastically intriguing character, but his eccentricities have made it difficult for him to fit in with others during his life. He does not have any family so there is no one to keep an eye on him.

Raymond has a very clear understanding of what has happened to him, but he is not one to complain. He is happy to go along with whatever processes he is asked to, and this must contribute in some way to his situation. When asked how he came to live in such a mess, he underplays it and says: "It was just laziness, I suppose."

Doubtless Raymond's isolated lifestyle meant he was susceptible to being overlooked, but as numerous services knew about him, surely he should not have been allowed to get to the point where he had maggots living in his leg?

Gina agrees: "I don't think Raymond needed to go through all of that. If we're going to stop other people getting into similar states then we need to act before we reach crisis point."

Liam Johnson (not his real name) became homeless and went on the run after getting involved in gang violence

Liam says things started to get difficult when his parents split up when he was 15. "I started arguing with my mum loads – she was taking her problems out on me. I left home when I was 16 because I'd had enough of the arguing. She didn't stop me."

Liam went straight to the council offices and they put him up in a hostel. He wasn't too anxious on his first night: "I just got really stoned so I didn't care." Once he'd settled in, he said it felt good to be on his own away from the arguing.

From then on his life became dominated by drugs, guns and violence. Shortly after he arrived at the hostel he started selling drugs. "I was buying for myself and asked the dealer if I could sell stuff on for him. I knew a lot of people who would buy and wanted to make some money."

Liam grew up surrounded by guns and drugs, but it was at this point that he really became embroiled in gang life. He went to prison for a couple of months, which he describes with a well-rehearsed nonchalance as: "All right – just boring really." His casual attitude does not seem to be indifference but rather a survival mechanism. Yet it is tinged with sadness.

He tells me: "At school I never thought I'd go to prison." He quickly adds: "But I did … I'm not really bothered."

Recently someone shot his friend in front of him. He narrowly escaped the same fate. He still doesn't know who it was that shot at them. "It could have been a few people. I'd upset a lot of people – robbing drugs and stuff. I knew they'd come after me again so I had to leave."

He fled from his home in Merseyside and was homeless again. "I ended up sleeping on the streets a few times. It wasn't nice but I wasn't bothered." The same caveat. I tell him I would find his life hard, but I've not grown up with violence. I ask if it bothers him that he has.

"I've been brought up in that world and I just think it's part of life. Everything happens for a reason. It's just the way it is. It has to happen to someone."

"But does it?", I ask.

"Apparently," he says.

He is now 20 years old and living in temporary accommodation again. I ask him about his hopes for the future.

He shrugs. "I haven't got any. Not any more." I ask him why. He shrugs again in his stoic way. "I don't know. I just don't. I take every day as it comes. I'll find out about the future when it gets here."