Limits placed on the freedom of people with dementia or brain injuries are not being properly recorded, according to a healthcare regulator.
The Care Quality Commission (CQC) said almost two-thirds of applications to restrict a person's liberty were not reported to it, as required by law.
The CQC said it could signal a lack of understanding or compliance with the Mental Capacity Act.
In some cases, patients had their freedom removed for months at a time.
Deprivation of Liberty Safeguards (DoLS) are used when someone lacks the capacity to make decisions for themselves.
Often, the safeguards allow a care worker to prevent someone with a mental disability or injury from leaving their care home, or to restrain them.
Almost 12,000 applications were made to restrict people's liberty between April 2011 and March 2012, an increase of 57% in two years.
Frida Sullivan was moved by her daughter, Jayne, into a care home in Cheam, south-west London, in 2009.
She hoped to be able to take her mother out on visits, sometimes back to her old house.
"In less than a week of her being there, I was told visits had to be severely restricted because she was causing problems," Jayne Sullivan said.
"The home blamed the outings and the visits, which I thought was ridiculous - they accepted her on those grounds. They said if I didn't do what I was told, they would kick her out."
Ms Sullivan said the health trust and social workers took the side of the care home.
"I had to do what I was told. I didn't know about Deprivation of Liberty Safeguards, nor the Court of Protection. I suspect most people don't," she said.
Three years after Frida was put in the home, the local government ombudsman found proper procedure - the DoLS - had not been followed.
The care home declined to comment.
Regional variations 'concerning'
When a care home or hospital applies to use the safeguards, the outcome must be reported to the healthcare regulator so it can ensure they are being applied appropriately.
But in England the CQC found only 37% of cases were properly recorded last year.
As a result, around 7,000 people were deprived of their liberty in a way that did not follow procedure.
The Welsh regulator is to start calculating a comparable figure from this year.
Lawyers representing people with mental disabilities suspect the numbers may be far higher because some care homes and hospitals are restraining people without using the safeguards.
Michael Furminger, a barrister specialising in community care law, said the possibility of people being deprived of their liberty without proper authority was worrying.
He said: "There are probably thousands of cases where either the care home do not know what they are doing, or do know but still do not make the application.
"At least if there is an application and a family is not happy, they can challenge it. But if there is a deprivation of liberty without authority, there is nothing to challenge."
Analysis by 5 live Investigates suggests someone in Leicestershire is more than 40 times more likely to be deprived of their liberty using the safeguards in the Mental Capacity Act than someone in Tower Hamlets.
A spokesman for Tower Hamlets council, which made four applications, said it was reviewing its use of the safeguards in recognition of its low figures.
Leicestershire County Council, which made 463 applications, said it was "proactive" in its safeguarding work.
A spokesman for the authority said: "We see these figures as a validation of good practice being in place, with care home managers, hospital staff and other professionals."
The Alzheimer's Society said the safeguards help protect human rights, but that it was concerned about the uneven use of them across the country.
George McNamara, the society's head of policy, said: "We think in some cases this may be as a result of the lack of awareness.
"It's important we clearly understand the reasons for this."
The Welsh healthcare regulator, the Care and Social Services Inspectorate Wales, said it was unsure whether high or low usage of the provisions represented good practice.
It said the regional variation suggests deprivation of liberty may have occurred in cases where it was not then properly recorded under the legislation.
Heather Hurford, the Care Quality Commission's head of policy, said the Court of Protection, which can be used to overturn Deprivation of Liberty Safeguards, was an "inaccessible mechanism".
She said: "There aren't courts set up all around the country. And in that sense the recourse families have is very different to the protections that are offered to people detained under the Mental Health Act, where tribunals can operate around the country. They'll convene within hospitals."
She also expressed concern that some care homes may be using blanket restrictions on residents rather than assessing individuals' needs.
Sarah Pickup, the president of the Association of Directors of Adult Social Services, said improved training was needed.
She said: "Social services have the lead for applying these safeguards and we recognise that legal literacy needs to improve in all workers and all fields."