One staff member has been sacked and seven suspended from one of England's largest care homes after an undercover probe by BBC Panorama found poor care.
The filming at the Old Deanery in Essex showed some residents being taunted, roughly handled and one was slapped.
The home said it was "shocked and saddened by the allegations".
Care minister Norman Lamb described the images as "absolutely disgusting" and said there "could be a role" for the use of CCTV in care homes.
Care Quality Commission figures seen by the BBC show over a third of homes that received warning notices since 2011 still do not meet basic standards.
Allegations of poor care and mistreatment at the 93-bed home in Braintree, where residents pay roughly £700 per week, were first raised by 11 whistle-blowers in August 2012.
Essex County Council put it on special measures for three months until concerns were addressed.
But secret filming by Panorama's undercover reporter over 36 shifts found many of the same sorts of issues reported a year earlier, including:
- a woman slapped by a care worker who had previously been complained about for her poor attitude towards residents
- the same woman, who has dementia and is partially paralysed after a stroke, was also repeatedly mocked and taunted by other care workers
- cries for assistance from a resident suffering a terminal illness ignored as she sought help for the toilet, and her call bell for assistance left unplugged on one occasion
- a resident bed-ridden with a chronic illness left lying in his own excrement after two care workers turned off his call bell without assisting him
Alex Lee, the reporter who conducted the undercover filming, said she saw "many good care workers trying their best" - but also saw some staff "mock, goad, taunt, roughly handle and ignore" elderly residents.
"Some were even left in their own mess for hours," she said.
Minister for care and support Norman Lamb said the images "turn your stomach" and there was a case for considering the use of cameras in care homes.
Speaking to BBC Radio 5 live, he said: "I think there is a real danger that if you think that you can create a good culture and compassionate care through CCTV you will fail completely.
"But I think it is one of the weapons that the Care Quality Commission should consider using and indeed they are considering.
"I think in specific cases where there are allegations or concerns about possible abuse or neglect then there could be a role for it."
Last November, while Panorama was undercover, the home was inspected by the regulator and passed for the first time in 18 months.
When the CQC revisited this February after being told about Panorama's findings, they found too few staff and some residents waiting an "unacceptably long time" for call bells to be answered.
Anglia Retirement Homes Ltd, which runs the Old Deanery, said the incidents involved a "small number of staff" and were not reflective of the high standards of care it demanded.
A statement said: "As soon as the new management team was made aware of the allegations we took immediate action.
"We hired an independent law firm to carry out a full investigation as a matter of urgency.
"Eight staff were immediately suspended, and have not returned to work, pending a full inquiry.
"Our priority remains the health and wellbeing of our residents and we have more than 200 dedicated members of staff who remain committed to the highest standards of care."
It added: "The care worker responsible for slapping a resident has been summarily dismissed."
The company was taken over by new owners in November 2013.
A former care assistant at another home, who became a whistle-blower, said she had experienced problems not being solved. Eileen Chubb runs a charity called Compassion in Care which supports people reporting misconduct in the industry.
She has had nearly 2,000 calls to her helpline in 14 years and she often found repeated complaints about the same problems in the same homes.
"Every day cases are coming in where there has been up to 15 staff, 20 staff, raising concerns, then six years later, more staff raising the same concerns again," she said.
The CQC said it would work with the care sector to improve standards, but it was determined to ensure problems were addressed.
Its new chief inspector of social care, Andrea Sutcliffe, said she was "shocked and really angry" about the poor care Panorama had found.
She said her "heart goes out" to those affected, but also to the "hundreds of thousands" of good care workers who had been let down by the "small minority".
"People shouldn't be getting into this business if they don't care," she said.
Asked if the CQC's systems were working, she said most care was good and the organisation would act on any concerns raised.
Panorama: Behind Closed Doors: Elderly Care Exposed on BBC One on Wednesday 30 April at 21:00 BST and then available in the UK on the BBC iPlayer.