Older people are suffering "disgraceful" home care including missed medication and confinement to soiled beds, an undercover investigation revealed.
Undercover researchers for the Which? consumer group reported missed visits, food out out of reach and vulnerable people left without a way of getting to the bathroom.
Which? asked 30 people or their carers to keep diaries over the course of a week in January detailing their experiences of home care, also known as domiciliary care, by paid workers.
One elderly woman was left alone in the dark for hours unable to find food or drink. Another was left without a walking frame, leaving her unable to get to the bathroom, while one man was not given vital diabetes medication, the watchdog said.
Which? declined to name the agencies involved, saying it wants to protect people who gave feedback.
One unnamed daughter reported: "They missed a day just after Christmas. They incorrectly entered into their database the days we didn't need care. I covered but mum didn't contact me until early evening, by which time she needed a lot of cleaning up. You wonder about the elderly with no relatives."
A son said: "There are times when dad, who is diabetic, hasn't had his insulin on time and it's vital medication. When I voiced my concerns to the care agency I was just told to find another agency."
Another daughter told the watchdog: "She can't see her sandwiches to eat them and hasn't touched her drinks as she can't see those either. I can't express how angry I feel at the carers. There is a printed note on the front door about putting a light on at 4pm as well as a note from me in the kitchen beside the care book. It is also in the care plan. What more can I do?"
Others did identify good service, with one son saying: "My mum's carer does things without being asked, such as tidying up, and will do extra things like brushing her shoes. Mum says she's a real carer."
However, a separate Which? survey found one of the most common complaints was missed and rushed visits, with relatives often left to step in.
Almost half of respondents (47%) able to answer a question about visits said at least one had been missed in the past six months, while 62% of those had not been warned in advance.
Which? said "in many cases" diarists reported a good service was provided only after complaining, with some family members being forced to make numerous phone calls and to have a "constant battle" with agencies.
Which? executive director Richard Lloyd said: "The Government can no longer claim to be shocked as report after report highlights the pitiful state of care for older people. If they are serious about ensuring vulnerable people are treated with dignity, then we must see real action because every day they delay is another day older people risk being neglected."
Care Quality Commission (CQC) chief executive Cynthia Bower said: "Home care is one of the most difficult areas of care to monitor because it is delivered behind closed doors which is why, starting next month, CQC will be carrying out a themed inspection programme of 250 providers of domiciliary care services.
"We will be focusing on dignity and respect, the safeguarding of people in vulnerable circumstances and how well supported and trained home care staff are to undertake these most important care tasks.
"We will use a range of ways of checking up on these services, including going into people's homes, contacting people who use services and their families and talking to local groups who represent the users of home care services."
Age UK charity director general Michelle Mitchell said: "While many careworkers work hard to provide compassionate care, the under-funding of the social care system is resulting in a serious reduction of domiciliary care, which can put both the health and dignity of older people at risk.
"Good home care must begin and end with the needs of individuals rather than focusing on a tick box of tasks to be completed within a set time."
UK Homecare Association spokesman Colin Angel said the report highlighted "the disturbing consequences of the commissioning of homecare by local councils".
"To meet the current stringent public sector spending cuts councils are making significant attempts to reduce the price they pay for care," he said.
"Homecare agencies repeatedly tell us that councils also allow less time for care to increasingly frail and elderly people. This raises serious questions about the ability of people to receive dignified, effective care, a situation which must be addressed nationally."
David Rogers, chairman of the Local Government Association's wellbeing board, said there was too little money in the system "and without fundamental reform the situation is only going to get worse".
"Local authorities are doing all they can to find solutions that don't impact on the services they can deliver to elderly and vulnerable residents and despite a 28% funding cut from Government, spending on adult services this year is expected to fall by just 2.5%, the lowest for any service area."
Care Services Minister Paul Burstow said: "We are funding work to put in place the first ever training standards for care assistants to raise the bar on quality.
"The best councils are arranging care that concentrates on delivering the outcomes people have a right to expect. Kindness, compassion, dignity and respect must be central to care, whoever provides it and wherever it is provided."