A quarter of home-care services provided to the elderly in England are failing to meet quality and safety standards, inspectors say.
More than 700,000 people above the age of 65 rely on home help for activities such as washing, dressing and eating.
But the Care Quality Commission found evidence of rushed appointments and botched assessments during its review of 250 services.
Campaigners said it was a sign of how much pressure the system was under.
On Monday, ministers announced plans for a £75,000 cap on the amount the elderly will have to pay for social care in England - only the poorest get it free.
The proposal aims to stop the elderly having to sell their homes to pay for care.
But the move will do nothing to get extra money into the system, something the sector believes is vital if the quality of services is going to be improved.
Home help services are considered essential in keeping people out of more expensive care homes.
The numbers getting help is pretty evenly split between self-funders and those who get council-funded care.
This review looked at the support being provided to both - and found too many were struggling to maintain standards.
A total of 26% failed on at least one standard.
One of the most common issues identified related to late, rushed or missed visits.
The regulator also highlighted assessments that had missed vital information, such as a diagnosis of diabetes, and care records that were incomplete, meaning problems such as pressure ulcers could be missed by carers.
Concerns were also raised about the way services were monitored and complaints handled.
The regulator said home care providers, many of which are private companies, needed to work closely with local authorities to remedy the problems.
It warned the problems identified could have a "significant impact" on the elderly, many of whom did not complain because of a fear of reprisals or loyalty to their carer.
The findings come after reports by both the consumer group Which? and the Equality and Human Rights Commission have criticised home care in the past 18 months.
Michelle Mitchell, of Age UK, said: "There must be a zero-tolerance attitude to poor, neglectful care."
The UK Homecare Association said it was pleasing the majority were meeting all the standards but said the sector was "not complacent" about the minority that were not.
A spokesman said some of the problems related to councils squeezing the amount of time they were willing to fund for visits.
Councillor David Rogers, of the Local Government Association, said were trying to "stamp out poor performance".
But he added: "As this report highlights, even the very best efforts of councils are not enough to avert the real and growing crisis we are facing in ensuring older people receive the care they deserve. The stark reality is that the current care system is underfunded and not fit for purpose."