Elderly and disabled people are increasingly relying on family and friends to care for them, inspectors have warned.
Some are having to go without care
Councils in England are restricting access to social services such as home care, day services and respite care.
The Commission for Social Care Inspection warned this was happening by default, and without debate.
The problem was being caused by increasing demands on social services and tension developing with the NHS.
Commission chairman Dame Denise Platt said services for those who qualified for care were actually improving.
But she said many people were being left to make their own arrangements because access to services was being tightened to include only those deemed to be in the most serious need.
She said: "In some cases people rely on family and friends, in others they pay for their own care.
"Some people have no option but to do without.
"It is also clear that external pressures on the sector are hindering progress in making services better for the people who use them.
"In particular NHS budget deficits are putting a strain on relationships and potentially under-mining essential partnerships."
The proportion of people who are over 65 is growing - over the next 20 years projections indicate it will rise by 53%.
The number of young disabled people is also increasing. Between 1975 and 2002 it rose by 62%.
To cope two-thirds of councils only offer support to those with substantial needs.
The Local Government Association predicts over the next few years no local authority will provide low or moderate support, including general home care support.
The Commission said family and friends are helping to fill some of the gaps.
Two million people received care from local councils during 2006.
Nearly six million people are classed as carers, with 1.5 million of those providing more than 20 hours of care per week.
The BBC's home editor Mark Easton said one in eight of the adult population were currently carers - but in a few decades it could become as many as one in five.
Dame Denise said: "They are doing this without the proper infra-structure in place.
"It is a complex sector, but they are often given no help navigating through it."
Neil Hunt, chief executive of the Alzheimer's Society, said the system was in crisis, and accused the government of being unwilling to provide sufficient funds to help people with serious medical conditions.
"Additional investment in the NHS has not been mirrored in social care. Inevitably the result has been that as need increases, local authorities skew what care there is available to people with high levels of need.
"Thousands of people who need extra help to remain independent are being ignored."
Age Concern's director general Gordon Lishman said: "This is a damning indictment of a social care system that is failing older people.
"Not providing services for people with so-called moderate needs causes much anguish for the individual - but can also result in much higher and more expensive care needs in the future."
The Department of Health said social care was improving in many areas.
But a spokesman added: "We are concerned about the potential effect of rising eligibility criteria.
"Local authorities need to put a greater emphasis on preventive services - helping people with lower needs to avoid admission to hospital or residential care."
Dame Denise said there needed to be a proper debate over what elderly people would be expected to pay for and what the responsibility of the state and families should be.