A hidden outbreak of sexual abuse in British hospitals has been disclosed in new figures revealing that more than 1,600 attacks were reported to police in the last three years.

Records obtained by the Guardian under the Freedom of Information Act show a 50% rise in reports of sexual violence in hospitals since 2011. It includes a total of at least 157 rape allegations.

Statistics on sexual abuse reports in hospitals were released by 38 out of 45 UK police forces. They document 1,615 attacks that are known about including cases on NHS wards, private clinics and other health centres. But prosecutors have said that up to 90% of sexual abuse goes unreported, suggesting the true figure could be much higher.

Last year the Metropolitan police received reports of 17 rapes and 124 other sex abuse crimes inside London hospitals.

Most police forces were unable to provide a firm breakdown of the types of hospitals where rapes and sexual abuse had been reported. However, the Met, which accounted for 20% of all reports, said the issue was a particular problem in mental health units, with a significant proportion of alleged victims identified as vulnerable due to mental health problems.

Luciana Berger, the shadow minister for public health, said the figures revealed a serious problem for the NHS and called for an urgent review of hospital security.

Individual cases of abuse in hospitals have been well documented but this is the first time the scale of the problem has been reported. The figures account for all reports of abuse, although a small number are understood to relate to historic attacks that occurred before 2011.

One victim described being groomed by her mental health support officer for five months. When she bumped into him years later it triggered a suicide attempt before she eventually reported him. However, the man resigned before the investigation concluded and authorities were unable to take action against him.

“I was in a vulnerable position at the time; certainly not in a position to consent to what he was doing,” she told the Guardian. “What have I gained by coming forward? Nothing. I’m just a person who has made allegations that haven’t been proven.”

In another case, a mental health patient described psychiatric hospitals as a “playground for predators”, after she was raped up to 60 times by a member of staff. The woman had been taken to Little Brook hospital in Kent after a breakdown and was warned she would be sectioned if she tried to leave. She described her ordeal to the BBC earlier this year. “At times I was on a very heavy amount of Valium, not to where I was unconscious, but the sedative combined with my already defeated self, I was like putty. He would pull the covers back, do what he had to do and leave, all very quickly. I didn’t move.”

When asked whether anyone else at the hospital knew about her abuse, the woman said: “I strongly suspect it can’t have been completely missed. I can’t believe how it could have been so frequent and not picked up on.”

She was eventually paid £100,000 compensation, but her attacker avoided jail after receiving a suspended sentence. A third case saw the care assistant Naraindrakoomar Sahodree jailed in 2010 for repeatedly raping a multiple sclerosis sufferer in her bed at a central London hospital. He had managed to get the job despite already being struck off the nurses’ register. In court, his victim said that Sahodree made sure she could not call for help by removing her warning buzzer.

Berger said: “A zero-tolerance approach to sexual abuse must be pursued in the NHS. All victims should feel safe to come forward and every incident properly dealt with by the police, courts and health service, to ensure every perpetrator is brought to justice.”

Berger said it was particularly worrying that people in mental health units appeared to be at high risk. “These are often some of the most vulnerable patients and their safety must be guaranteed,” she said. “Ministers must order an immediate review of security, with a focus on mental health units.”

Nat Miles, senior policy and campaigns officer at Mind, said: “It’s completely unacceptable that sexual abuse is so prevalent within mental health units. Many people told us they are often seen as vulnerable and therefore an easy target by perpetrators, and are more easily discredited and less likely to be taken seriously if they report a crime.” She added: “Too often, crimes on wards are dealt with internally and not reported to police. It’s vital that frontline staff are adequately trained, so crimes are taken seriously, and dealt with quickly and appropriately.”

An NHS England spokesperson said: “It is of course essential that both NHS and independent hospitals do everything to ensure that patients are safe and feel safe in their premises, and where concerns arise the police must be able to bring to bear the full force of the law.”

Case study: ‘All i want is an apology’

Sue, a mental health patient, describes the abuse she suffered in an NHS support centre.

“He started very subtly, at the time I felt like a genuine relationship. He would walk close to me and say my perfume smelled nice. Then we started holding hands and meeting up out of his working hours. Sometimes I would go and see him when he was working on a Sunday morning and we would go down to the basement together.

“I had just been diagnosed with clinical depression and anxiety and he was my support worker. I was in a vulnerable position at the time; certainly not in a position to consent to what he was doing. It went on over about five months until he abruptly ended it with me one day.

“There was sexual touching, there was hands up the clothes. Ever since, I’ve felt that I don’t want another man to touch me again: that’s what he’s left me with.

“I knew that what he was doing was inappropriate, but I didn’t realise the effect he was having on me until after we broke up. He was part of the crisis team, so if I felt that I needed support after office hours I knew that if I dialled the number there would be every likelihood that he would be the one answering the phone. I had great difficulty trusting any member of the mental health team at all.

“I didn’t dare say anything to anybody. I know it’s not my fault, but I still think it’s my fault. To this day I still partly blame myself.

“Earlier this year, I bumped into him in a supermarket. He ignored me. I wasn’t in a good place mentally at the time. Just seeing him triggered extreme distress and anger. I tried to get help, but I couldn’t explain the situation to them. I attempted suicide by the end of the day.

“When I eventually reported it, it took 22 weeks for the health authorities to investigate. At the end, there was an independent hearing where he could have his say, but he resigned just beforehand. So what have I gained by coming forward? Nothing. I’m just a person who has made allegations that haven’t been proven.

“The police wanted to interview me, but I was in pieces at that point and I couldn’t face a police interview as well as everything else. I think they were hoping that another victim would come forward, because it was just my word against his.

“Even when I sent off a statement, I thought: ‘Am I was going to be believed? I’m just a nutty woman and he’s a professional.’, and I have no solid proof that these things happened. When you have a mental disorder you get disbelieved in many shapes and forms, so why should they believe you with this? It’s embarrassing, you feel ashamed, you feel guilty. I was just mortified to have to speak to them about it. They don’t make it easy for people; the whole thing requires a lot of strength.

“The whole experience has worsened my mental health; I’ve gone downhill massively. It’s like they’ve come along with a giant spoon, stirred up all the memories and left me to deal with it. I’ve made repeated suicide attempts and I’ve become more and more desperate. At the moment it feels like the lowest point ever in my life.

“Until I started talking about it, I didn’t realise how deeply and badly those five months had affected me. To date, I still haven’t had a formal, written comeback about my complaint – not even an apology. That’s all I want; that would make the biggest difference to me.”

Sue’s name has been changed