Hundreds of people with a learning disability and/or autism (LDA) are being held in mental health units even though they have been identified as no longer needing inpatient care.
According to analysis by Sky News of published NHS data, 635 of the 2,250 with an LDA currently detained in one of these units could be moved to community-based care.
The figures for September 2019 show 130 of the 635 have had their discharge from hospital delayed. This is the highest number since March 2015.
In a growing number of cases the delays are caused by a lack of suitable housing provision and social care support in the community.
Of the 130 people whose discharge was delayed, 29% were awaiting a residential care home place, 35% were affected by a lack of suitable housing provision and 16% from a lack of social care support.
Commenting on the figures, Julie Newcombe, co-founder of Rightful Lives, a campaign group set up to protect the human rights of autistic people and those with a learning disability, told Sky News: "We know what the problems are for why people are not able to move out of hospitals and we know what the solutions are.
"The issue is getting the solutions in place. Without accountability, trust, ringfenced funding for social care and proper respect for human rights laws, it feels as if we will never get where we need to be."
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The joint committee on human rights (JCHR) recently published a damning report on the detention of young people with learning disabilities and autism warning that many are having their human rights breached by the "horrific" conditions of mental health hospitals that are inflicting "terrible suffering" upon detainees.
The government was told it must urgently overhaul how the facilities are inspected to improve standards and protect those who are meant to be being cared for.
The JCHR found the detention of people with learning disabilities and autism was "often inappropriate" and "causes suffering and does long-term damage".
Health Secretary Matt Hancock promised earlier to review the discharge and care plan of all 2,250 people with LDA detained in these units over the next 12 months.
Mr Hancock said: "For those living with learning disabilities and autistic people, the current system can leave them in isolation for long periods of time, with no prospect of release into the community.
"I am determined to put this right and today we are committing to reviewing the care of every patient with learning disability and autism over the next 12 months – alongside a clear plan to get them discharged back into their homes and communities. I have also asked for advice on separating out the law regarding those with learning disabilities and autism from the law regarding mental health.
"This will start with those in the most restrictive settings. I am delighted Baroness Hollins has agreed to chair our new independent panel to make sure that they are supported to discharge as quickly as possible.
"Baroness Hollins brings a wealth of experience and will provide the right level of scrutiny and challenge to ensure that everything possible is done to improve care on the ground."