Disjointed health and social care services are placing increasing pressure on A&E departments in England, the independent health regulator has warned.
A report by the Care Quality Commission (CQC) suggests there is growing "care injustice" in access to services across the country.
It said "ineffective collaboration" is driving demand for emergency care, with struggling hospitals often "symptomatic of a struggling local health and care system".
The regulator warned unmet social care need is continuing to rise and in some areas a "tipping point" has been reached, as people fail to get the quality of care they need.
Without changes to the way health and social care systems are funded, an increasing number of people will be failed by the system, it said.
Charity Age UK criticised the "Russian Roulette" for care and called for equal access across the country.
The overall quality of health and care services has been maintained since last year, the CQC State of Care report shows, which the regulator said is credit to the "resilience" of the system.
Inspectors rated 79% of adult social care services as good, up slightly from 78% last year, while 17% were rated as requiring improvement, down from 19%.
Less than a third (31%) of NHS acute hospital services were rated as requires improvement, compared to 37% in 2017.
However the CQC said the experience of care varies significantly depending on where an individual lives, which is often linked to "ineffective collaboration" between health and care services.
This can lead to increased demand for emergency services.
"It means a struggling acute hospital can be symptomatic of a struggling local health and care system," the report said.
The CQC said emergency departments are the most likely to be rated as requiring improvement (41%) or inadequate (7%) and noted that July saw the highest number of A&E attendances on record.
Ian Trenholm (pictured), chief executive of the CQC, said incentives are needed "that bring local health and care leaders together, rather than drive them apart".
"This is not so much a 'postcode lottery' as an 'integration lottery'," he said.
Calling for changes to the way services are funded, Mr Trenholm said: "The alternative is a future in which care injustice will increase and where some people will be failed by the services that are meant to support them, with their health and quality of life suffering as a result."
Peter Wyman, chairman of the CQC, said the "fragility of the adult social care market" was also a "big concern".
"Two years ago, we warned that social care was 'approaching a tipping point' - as unmet need continues to rise, this tipping point has already been reached for some people who are not getting the good quality care they need," he said.
"It is increasingly clear without a long-term funding settlement for adult social care, the additional funding for the NHS will be spent treating people with complex conditions for whom care in the community would have been more effective both in terms of their health and wellbeing and use of public money."
Caroline Abrahams, charity director at Age UK, said it is "increasingly pot luck" whether elderly people receive good, or any, service.
"Nowadays we even hear of variations within areas as well as between them, both as regards access to care and also how well that care is joined up with other essential provision like district nursing and physiotherapy," she said.
"A good care service can make all the difference in the world for an older person in declining health and it's wrong that they should have to play Russian Roulette with something so vital."
A Department of Health and Social Care spokeswoman said: "It is testament to our hardworking, dedicated NHS and social care staff that the vast majority of patients continue to receive good, safe care and many parts of the NHS have improved since this time last year.
"We want the NHS to be the safest healthcare system in the world - and this starts by ensuring every single patient in this country receives the highest quality of care, no matter where they live.
"This is backed by our long term plan to guarantee the future of the NHS with an extra £20.5 billion a year by 2023/24.
"We are addressing immediate pressures on the NHS this winter with an extra £420 million to redevelop A&Es, improve emergency care and help get patients home quicker, freeing up hospital beds for those who need them."
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