The Government has ordered an urgent review into the "inhumane" abuse of people with learning disabilities at a residential hospital.
Police arrested four people after secret filming by BBC Panorama showed vulnerable adults at Winterbourne View, in Bristol, being punched, slapped and taunted by carers.
Three men, aged 42, 30 and 25, and a 24-year-old woman have now been released on bail by Avon and Somerset police.
Care services minister Paul Burstow ordered a "thorough examination" of the role of the Care Quality Commission (CQC) - the social care services regulator - and local authorities in the case.
He also asked the CQC to carry out a series of unannounced inspections of similar services.
Thirteen members of staff, including two managers, have been suspended by the hospital's owners Castlebeck.
During five weeks of undercover filming in February and March, patients were seen being pinned down, slapped, doused in cold water and repeatedly taunted and teased.
Mr Burstow said: "The abuse of people with learning disabilities at Winterbourne View uncovered by Panorama is shocking.
"There can be no place for such inhumanity in care services. I have already asked CQC to undertake a series of unannounced inspections of similar services.
"There have been failures of inspection and adult protection which have exposed people to appalling abuse.
"I have already ordered a thorough examination of the roles of both CQC and the local authorities in this case. I am determined to strengthen the system of safeguarding to protect vulnerable adults from abuse."
The Prime Minister's spokesman said the case was "clearly very shocking" but insisted it was too early to draw wider conclusions.
Asked if CQC had sufficient resources, he told reporters: "Clearly there have been failures in this case. We need to look at that before drawing any conclusions."
Winterbourne View is a privately-run hospital which cares for up to 24 patients, employs around 50 members of staff and is funded by taxpayers.
Mark Goldring, chief executive of learning disability charity Mencap, called for the hospital to be closed down.
He told BBC Radio 4's Today programme that the treatment of patients was "horrific" and "did feel like torture".
"The behaviour of the individuals was cruel and barbaric and the management seemed to be either complicit or non-existent," he said.
"So it was scandalous and the home should be shut down."
Castlebeck emphasised its "distress" at the allegations.
Chief executive officer Lee Reed said: "I was shocked, disgusted and ashamed by what I saw on Panorama.
"Having spent my entire career in health and social care, I intend to leave no stone unturned to ensure that this type of horrific event is never allowed to happen again."
The company confirmed a former nurse had made a complaint about the quality of care to hospital managers last October. But neither the chief executive nor board members were made aware of it due to "delays".
The CQC apologised for also failing to respond to a complaint made by the same person in December.
The regulator said last night's Panorama programme highlighted "serious abuse and appalling standards of care" at Winterbourne View.
"Following an internal review, we recognise that there were indications of problems at this hospital which should have led to us taking action sooner.
"We apologise to those who have been let down by our failure to act more swiftly to address the appalling treatment that people at this hospital were subjected to."
CQC was contacted by the whistleblower on December 6 but said it believed these concerns were already being examined by the local authority.
"However, we recognise that, had we contacted the whistleblower ourselves directly after we received the email, we would have been alerted to the seriousness of the situation and moved swiftly to inspect the hospital," it said.
An Avon and Somerset Police spokesman said: "Police can confirm that four people have been arrested in connection with inquiries linked to allegations of abuse and mistreating of patients at the Winterbourne View Hospital in Hambrook.
"Three men, aged 42, 30 and 25, and a woman, aged 24 years, have been arrested on suspicion of assault/mistreatment of patients under the Mental Capacity Act.
"All four have been released on police bail, pending further inquiries."Reuse content