An 84-year-old woman with Alzheimer's disease is at the centre of a landmark legal case being heard by Law Lords.
The ruling could have implications for up to 300,000 people
The woman, known only as YL, has been threatened with eviction from the private care home she lives in.
She does not have the same protection under the Human Rights Act as she would if she were in a council-run home.
But - in a case which could affect 300,000 private care home residents - her lawyers say she should be protected because the council pays for her.
Such residents are currently unprotected by the Act, which covers public authorities and those performing public functions.
In Mrs YL's case, her lawyers say there has been an "irretrievable breakdown" in the relationship between her family and her care home, which is run by Southern Cross Healthcare Ltd.
It has been alleged that her daughter, who pays additional top-up fees, had broken a fitting in the home and had been aggressive to staff.
Her husband is also alleged to have been violent towards his wife.
Mrs YL is currently being allowed to stay in the home after arrangements were made for supervised visits from her family, but her lawyers say the threat to evict her could be resurrected at any time.
Medical experts have said moving her would be a "grave risk" to her health.
If her case is successful, private care home residents could be entitled to rights such as the "right to respect for private and family life", the "prohibition of inhuman and degrading treatment" and the "right to a peaceful enjoyment of possessions".
The Lord Chancellor, Lord Falconer, is backing Mrs YL's case.
In January, three appeal judges rejected the idea that a private care home was exercising a public function when it looked after people referred and funded by the local authority.
But it said Mrs YL's case should be referred to the highest court possible because of its public importance.
Gordon Lishman, director general of Age Concern England, said: "We hope that this test case will close this loophole in the law so that vulnerable older people are equally protected by the Human Rights Act."
But Sheila Scott, chief executive of the National Care Association, said: "We have always believed that it is for local government to arrange services to be provided for people in need of care in the independent sector and that there is already significant, robust and pertinent legislation in place within the Care Standards Act to protect people living in care homes from abuse and neglect."
The hearing is set to last three days, but the decision is expected to come at a later date.