Five years ago, I met the actor Samantha Morton to discuss a film she had made based on her life in a children's home. It was a spare, shocking depiction of a little girl beaten, physically and emotionally, into silence. The Unloved was, and remains, the only film she has directed. At the time, Morton said that if she had included everything that had happened in her childhood, no one would have believed her. I asked her what she meant. "Violence, sexual abuse, torture," she said, but refused to be drawn further.

At the end of the interview, she said she sometimes questioned whether acting was the right career for her; she wondered if she shouldn't be in social work or politics. "Some people have had a tough time, they've been in care or whatever, and they leave it behind them. Off they go and ride into the sunset with a nice house." But she wasn't capable of that. "I'm always going back. It's still so much part of me."

Since then, we've kept in touch. Morton has continued to act, had a third child and campaigned against cuts in children's services. Two weeks ago, she phoned to say she hadn't been able to sleep for a week after hearing the revelations about child sexual abuse in Rotherham – that 1,400 children, many of them in care, had been abused between 1997 and 2013. "I was doing OK," she said, "and then suddenly the Rotherham thing comes up." The report had dredged up terrible, semi-dormant memories. The danger now, Morton thought, was that Rotherham would be written off as one bad apple, an exception to the rule. But from her experience, it isn't, and she wanted to talk for the first time about the sexual abuse she experienced in care. We agreed to meet in London a couple of days later.

She is nervous when we do meet, and exhausted. Her baby is only five months old and she is still breastfeeding. (Her eldest daughter is now 14.) But, tired though she is, you get the sense that if she doesn't do this, her history could suffocate her. "When you talk to people who have survived a war, they're left with post-traumatic stress syndrome. You're left with this kind of ghost, it's always with you. And I think when you're in care…" She stops. "Even though I'm 37, I still feel that I'm a kid in care, and it feels like that – like you've been in a war."

Morton spent most of her childhood in foster homes or children's homes. Her parents, who separated when she was two, had nine children between them. Her father was violent and spent time in prison; her mother had a breakdown and couldn't cope. Her stepfather, now dead, was an alcoholic who served time for attempted murder. Despite everything, Morton insists she still loves her parents: she describes her relationship with her mother as "complex" but extremely close.

Morton was moved permanently into a council-run children's home, Redtiles in Nottingham, at the age of 11. By that age, foster parents were hard to come by: older children were regarded as trouble. In fact, she says, she was anything but, even if she became so later on. "I was very innocent and went to church. People called me a Bible-basher, so I was just scared of getting bullied, really." She was terrified when she was sent to Redtiles under an interim care order. "I knew from when I was very little what care order I was on – who owned me, why they owned me, and what rights I had. Because every little girl wants to live with her mummy, and I wasn't allowed, so I needed to understand why." Her father had custody of the children, but when he had a breakdown or was jailed, she would be sent to foster or care homes.

One of her older sisters had already been in a children's home and Morton had heard terrible stories. Still, she ended up loving most of her three years at Redtiles. For the first time in her life, she felt as if she belonged. It was a small home with just nine children, and they looked out for each other.

Even now, she doesn't really understand how the abuse started. What she does know is that it followed a very familiar pattern: she was befriended by her abusers, they gave her treats, bought her nice things, made her feel special. "You're the one that gets the extra portion of food, or gets the trip into town." Before she knew it, things turned nasty. She was sexually abused by two residential care workers, at first individually. Then one night, when she was 13, they both assaulted her in her bedroom. Afterwards, they never said anything about it to her, and she never said anything about it to them.

Did she tell her friends? "Not immediately. I was embarrassed and the people that did what they did to me were really…" Her sentences become broken. "I thought they were really nice people, so I was actually really shocked when it happened. And, ultimately, nobody would have believed me, because they're the coolest, nicest people. People with the best trainers, the nicest car, this, that. It's a shock when someone does things to you, you know, things you're not expecting. It isn't that people suddenly become the bogeymen. Abuse of children is gradual – this is why we now understand the term grooming. But no, I didn't go to anybody immediately because – how weird is this? – I didn't want to get them into trouble. I didn't want them to lose their jobs."

Eventually, she told social workers, who did nothing. "They had clipboards and were always moving on to the next question. There was no support, no offer of counselling, no wanting to delve deeper." She has spent years trying to understand why they failed to react and has come to the conclusion that it was so common, they didn't think there was anything to be done. "Maybe they just assumed I had been abused already, or was being anyway. I'd say 90% of my friends in the home had been sexually abused, but they might not be in there because of that. They might be there because they'd been shoplifting a lot, or nicking cars."

A few weeks after the assault, she told her mother, who took her to Oxclose Lane police station in Nottingham. Officers took a statement, and that night she was removed from Redtiles and placed in another home, Wollaton House, also in Nottingham. No further action was taken, and both men stayed in their jobs.

Morton was devastated. "I was never allowed to go back to the home, so I didn't get to say goodbye to the people I loved." Did she feel she was being punished for having gone to the police? "Yes, massively – that I'd betrayed that place and those people that I loved, and some of the people that loved me, maybe." The actor returned to the home years later, once she was sure the abusers had left. Some of the staff she had been close to were still there, and told her how proud they were: by then, she had been nominated for two Oscars. She was told the abusers no longer worked in the care system.

Had she expected them to go to prison? "I didn't think about prison when I was a kid. I didn't want any harm to come to them. I was too little to understand the ramifications. I just knew I didn't like what they were doing, and I didn't want them to do it to anyone else. I knew that it was wrong. I just wanted it to not ever happen again, and for me to be in Redtiles and be happy."

I ask if other children in the home were being sexually abused by social workers. "Some. Not all." She corrects me. "It's important you say 'residential social workers' because to become a social worker, you have to train, you have to get a degree; you work very hard. But you could be a residential social worker without a huge amount of training." Many of these workers were in their late teens. So it was basically kids looking after kids? "Yeah, but they can lock the fridge and lock the cupboard and turn off the TV."

Morton believes there is an inevitability about the abuse of children in care. "You have children living with their abusers. These people are feeding you, they're monitoring the home, they're sleeping in the room next to yours." Staff carried keys that gave them access to every bedroom. "When you hear those keys, it's a bit like in prison, really. For years, I didn't know why I'd get panic attacks when I heard keys."

When contacted by the Guardian, Steve Edwards, Nottinghamshire county council's service director for children's social care, said: "We take all allegations of child abuse, current or historic, extremely seriously. We will fully support any police investigation and would encourage the person in question to contact us directly to discuss her concerns." I also spoke to Nottingham city council, who told me: "Redtiles no longer exists. Children's residential care has changed significantly and is now subject to tight regulation and monitoring."

Morton wants to make one thing clear: that some social workers and residential care workers were wonderful. She talks about one who noticed she was being groomed by a Sunday school teacher and put a stop to it. The final home she lived in, Bracken House, had a terrible reputation and was eventually shut down, but she can't speak highly enough of it. "The staff were just remarkable and worked incredibly hard with not very much. The resources were prehistoric. We didn't have nice things, or furniture, or a TV that worked properly, but the staff were incredibly caring." She talks about the young men who would hang around outside the homes, apparently unemployed, but driving BMWs and XR3is. What were they offering? "Drugs, alcohol, respite from the home, somewhere to stay."

Like many children in care, Morton was often arrested, and says on these occasions she would talk to the police about her experiences of abuse in the care system. "You'd get arrested for, say, a public outburst of anger, a fight. You might be drunk, then you'd get taken to the police cells and locked up, and in that process the anger will come out. You would tell a police officer, and they would go: this has got to stop, have you told your social worker?" And did it stop? She shakes her head. "What chance is there if the people investigating the residential social workers are their colleagues?" On one occasion, she was told by police that their hands were tied because of social services. She didn't know what they meant, but thinks she does now: there was just no will to investigate. "A lot of people who abused my friends were people in very, very top jobs within the social services. Nottingham in the 80s was rife with that." Does she think these people deliberately sought out jobs with vulnerable children? "Yes, absolutely. I know they did."

There was physical abuse by staff, too, Morton says. "I was once punched in the face by a young male residential social worker because I told him to eff off." How old was she? "Fourteen. A fully-fledged punch by a man in the face. I was being incredibly cheeky, so that's what I got. You can complain to the police until you're blue in the face, but they're so used to violence in children's homes that they don't want to be seen, if you like, as the therapist. They're often called out to these disturbances: 'Oh, there's another barricading session going on in this home, and we'll just stay back.' It's like a domestic."

When contacted by the Guardian, Superintendent Helen Chamberlain, head of public protection at Nottinghamshire police, said: "We take all allegations of sexual abuse very seriously and investigate them to the fullest extent of our powers. We are currently liaising with the individual in question in a bid to understand what may have happened to her when she was a child. She can be assured that, where appropriate, we will seek to take action."

The home Morton was sent to after Redtiles (Wollaton House, now closed) was horrific, she says. Here, she was physically rather than sexually abused, but it was her worst experience in care. Technically, she was there for a year, but she ran away most nights, often sleeping rough. She was by this time no longer a young Bible-basher, but an angry, troubled teen ("I was furious from the age of 13 onwards"). She was convicted on a charge of threats to kill, after picking up a knife in an argument with a girl who had been bullying her, and sentenced to 18 weeks at an attendance centre. It was the wake-up call she needed, and she began to get a grip on her life. As soon as she was legally entitled to, aged 16, she embraced her independence and headed to London. Within months, she was acting in the television series Soldier Soldier, then Cracker and Band Of Gold – all while she was still in her teens. "Acting can suit certain people," she says, "because you're used to moving on all the time and making new families on each new set."

Social services neglected her just as thoroughly after she left care, she says. From the day she turned 16, it was as if she had never existed: no monitoring, no follow-up, no records kept. She might have been selling sex on the streets for all they knew, and some of her friends did. Was she the resilient type? "Not always, no. And I think that's the misconception: 'Oh, she'll be all right, she's strong.' And that can be your downfall, because people don't realise how vulnerable you are if you're tough."

Much of the coverage of the Rotherham scandal has focused on the fact that many of the abusers were of Pakistani origin. Were the young men who hung about Nottingham's children's homes in the 1980s from any particular background? "No, just local boys, mainly white." Abusers come in all shapes and sizes, she says; they simply reflect the local demographic. "Redtiles is in a predominantly white area. I suppose if the home had been in Hyson Green, maybe it would have been Pakistani men. I don't think it was race-specific. Not at all."

In many ways, Morton is one of the lucky ones. She has a job she loves, a loving family, friends and colleagues who will listen to her. So many of the people she knows were destroyed by their time in care. "I've done well, but I just think every day about the people out there that didn't, that don't survive and can't survive for whatever reason, who fall into patterns of alcohol abuse, drug abuse, homelessness, in and out of prison. And you trace it all the way back, and it can be something like sexual abuse that is a trigger. I had one friend who set fire to herself in the street and she's now in a mental home. 'Do you believe me, do you believe me, do you believe me?' she'd always say."

There are practical steps the authorities could be taking to minimise risk, she argues. First of all, take private homes out of the equation: however vulnerable to abuse state-run children's homes are, the private ones are even more so. "You need to take profit out of it. If people can make a profit out of the vulnerability of young people, that's wrong from the start. The minute you bring money into it, you're going to attract the wrong people. I want to see money put back into care. Money for retraining, money for counselling services for young people."

Perhaps the most important change she'd like to see is the bar raised for residential care workers. They should all be qualified, she says, and the pay should be better. "If you make it a job to feel proud of, you're going to get a better standard of care – people going into it because it's a passion, because they want to work with kids in that way."

As for bringing perpetrators to justice, she is convinced that at best it was never a priority and at worst there has long been a conspiracy of silence. "I believe there is institutional prejudice against looked-after young people within the police forces across the country. It has been deep-rooted for all of my life."

Does she find it easier to trust people these days? "Yes. And I refuse to be jaded by people out there who maybe want to harm me or make money out of me. I mean, my dad sold loads of stories about me." Half of them are rubbish, she says. Is he still selling stories? She laughs. "I don't know. We'll have to find out after this, hey?"

Is she still traumatised by her childhood? "I wouldn't say that I live in a constant state of illness, but I do think that when you have been sexually or physically abused, it is a life sentence. It does stay with you for ever. Trauma is like grief. You can be fine for four or five years, then it comes back and hits you like it happened the day before." She pauses. "But then you can heal, you can find ways to love yourself, to be a valid member of society, to give back."

She looks done in. It is partly being up at night with the baby, and partly talking about all this. She says she's glad she has, though – she thinks she has a responsibility. I ask who she feels angriest with now: her abusers, the police, the social services? "Social services," she says instantly. "They had a duty of care – not only a social duty of care, but a legal obligation to take care of me, and they didn't. They failed miserably. But I survived. I'm here to tell the tale. I don't want this to happen to anyone else."