England and Wales have 5,000 medium secure mental health beds
There were at least 94 escapes from medium and low secure psychiatric hospitals and escorting staff last year, a BBC investigation has found.
Some of the units held patients who had committed serious and violent crimes.
Last year, Darren Harkin, a convicted killer, escaped from Hayes Hospital, a secure private hospital near Bristol, and raped a 14-year-old girl.
The former chief inspector of prisons, Sir David Ramsbotham, described the figures as horrifying.
Using the Freedom of Information Act, the Today programme found that at least 94 patients had escaped from medium and low secure psychiatric units in England and Wales and from escorting staff last year.
Four patients remain at large. That compares with just five escapes from prisons and escorting staff in 2007.
ESCAPES IN 2007
94 escapes from medium and low secure psychiatric units
Only five escapes from prisons
England and Wales have almost 5,000 medium secure mental health beds
3,022 NHS beds
1,913 independent sector beds
These figures record only escapes from NHS institutions
Sir David Ramsbotham said the figures were a wake-up call to the government.
He said: "It is a horrifying figure of course, but not one that surprises me because the medium and low secure units in the NHS do not have same degree of security a prison does."
On Monday, Judge Nicholas Cooke QC sentenced Harkin to be held at the maximum security hospital Broadmoor.
Sentencing Harkin, the judge said alarm bells ought to have sounded regarding Harkin's deteriorating behaviour in the weeks leading up to his escape.
Harkin was 12 when he killed his baby stepbrother in a violent knife attack.
Originally sent to prison, he was moved to a medium secure unit and finally to the low security Hayes Hospital, run by the National Autistic Society, before he escaped in February.
During his escape he raped a 14-year-old girl at knifepoint. Her father has grave concerns that Harkin was housed in the unit.
The National Autistic Society runs The Hayes
"I do feel that the local community is at risk while people with that type of history are kept in a unit which is clearly fairly easy to get out of if they wish to do so. I mean someone with his previous criminal record and obvious mental instability…"
"When we moved here it was a particularly nice and relatively safe area to live in. It's just unbelievable that something like this could occur. Obviously it's had a massive impact on my daughter."
Two other cases which have raised security concerns at the Hayes, included an incident in which patient Tamer Mahmood was taken to St Werburghs City Farm - a place popular with families and schoolchildren.
The farm said it was not informed he was on the sex offenders register and despite being accompanied by staff Mahmood absconded for 17 hours.
The Hayes Hospital admitted they may have been wrong not to inform the farm of the patient's criminal history on this occasion. Even so, they said they might in future withhold such information depending on individual circumstances.
Earlier in March another patient from the Hayes, who was allowed a pint at a local pub every week under supervision, became aggressive.
The Hayes is not a prison. It is a hospital which specialises in working with people with autistic spectrum disorders. Our primary aim is therapeutic, to help people grow in their independence
Carol Povey, National Autistic Society
Following these three incidents Carol Povey, head of adult services at the National Autistic Society, was asked whether security should be stepped up, but said this was not necessarily the best course of action.
"The Hayes is not a prison. It is a hospital which specialises in working with people with autistic spectrum disorders. Our primary aim is therapeutic, to help people grow in their independence," she said.
"People who live here are here because they've been assessed.
"There has been an incident which was absolutely tragic, but we're working with complex people. We try to get the balance between therapy and security and it's extremely difficult to do that."
In court, Judge Nicholas Cooke QC asked how Darren Harkin had managed to meet Home Office criteria to be housed in a low secure unit, having absconded three times from his medium secure unit and displayed destructive and aggressive behaviour.
The judge questioned why the hospital had not contemplated returning him to a higher secure unit when his behaviour become more disturbed and he demonstrated a danger to female staff, just before he escaped.
The judge was also concerned about Harkin's considerable collection of horror and pornographic films in the Hayes unit. The hospital has since said that despite reviewing policy, patients will still be allowed legally available material based on individual circumstances.
'Treatment and recovery'
At Runwell secure psychiatric hospital in Essex there is a regulation perimeter fence but patients are not locked in their rooms, and there are no bars on the windows. Security here is much lower than at an ordinary prison even though most of Runwell's patients have also committed crimes.
"I think what we try and create is a homely experience within a secure service. We are aware of the issues around security but fundamentally this is about treatment and recovery," Oliver Shanley, director of nursing, said.
One senior nurse from a medium secure unit who has worked in the field for more than 10 years expressed his concerns about security.
"One of the units I worked in recently was not fit for purpose.
Runwell hospital has a perimeter fence
"We said to our trust that we wanted to have bars put on windows that patients could possibly escape from and managers didn't do it because they said it was aesthetically unpleasing and could stifle the therapeutic nature of the unit and they didn't have the finances - until three people broke out and then they had the finances to sort it out."
The Ministry of Justice defines escape as when a prisoner unlawfully gains their liberty by breaching a secure perimeter. A prisoner escapes from escort when they are able to pass beyond the control of escorting staff.
Barry Topping-Morris, until recently an adviser on mental health policy and the chair of the Mental Health Nursing Society, said that nurses are working in difficult circumstances but argued that swift improvements need to be made.
"The Department of Health and the Ministry of Justice have recognised that standards across medium secure units are variable.
"In my opinion some services are built to a very high physical specification but not run very well and in other examples where the physical specification could be considered as weak that is compensated by there being excellent practice within such a service."
These variations continue, he believes, despite new security standards being introduced last year.
Liberal Democrat health spokesman Norman Lamb said the figures were "a shocking demonstration of the lack of attention and investment in mental health services in this country".
Escapes from psychiatric hospitals 2007
Figures for low and medium secure units
Name of unit
Barnet, Enfield and Haringey Mental Health Trust
Birmingham & Solihull Mental Health NHS Fdtn Trust
Bradford District Care Trust
Calderstones NHS Trust
Derbyshire Mental Health Services NHS Trust
Devon Partnership NHS Trust
North Essex Partnership NHS Foundation Trust
South Essex Partnership NHS Foundation Trust
Hampshire Partnership NHS Trust
Hertfordshire Partnership NHS Foundation Trust
Lancashire Care NHS Foundation Trust
Lincolnshire Partnership NHS Foundation Trust
Central and North West London NHS Foundation Trust
West London Mental Health NHS Trust
Greater Manchester West MH NHS Foundation Trust
Mersey Care NHS Trust
Norfolk & Waveney Mental Health NHS Fdtn Trust
Northumberland Tyne and Wear NHS Trust
Oxleas NHS Foundation Trust
Sheffield Health & Social Care NHS Foundation Trust
Suffolk Mental Health Partnership NHS Trust
Tees Esk and Wear Valleys NHS Foundation Trust
South West Yorkshire Mental Health NHS Trust
Cardiff and Vale NHS Trust
Source: Today Programme using Freedom of Information Act
Note: Earlier versions of this story reported that there had been 116 escapes rather than 94. Calderstones NHS Trust subsequently said it had misinterpreted the BBC's request for information and revised its response from 23 escapees to one person. The story has been amended to reflect this.
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