Nearly nine in 10 GPs questioned for a survey said they feared that social care services were not providing sufficient care for patients leading to extra pressure on surgeries and other parts of the health system.
The poll found that almost three-quarters (71%) believed care services would worsen over the next two to three years, while more than nine out of 10 GPs (92%) said they did not believe there was a sufficient level of care provided to offer patients an alternative to going to A&E.
It also found that 85% believed that cuts to local authority budgets meant there were less care and support services available now than five years ago, slightly less than the 88% who said they did not believe social care services currently provided a sufficient level of care.
The survey of 830 GPs was commissioned by the Care and Support Alliance (CSA) - a coalition of more than 75 major charities who are campaigning for a better funded care system.
The CSA said the "care system is on its knees", with demand going up as more people are living longer at the same time as chronic underfunding is seeing fewer and fewer people getting support.
Around £3.5 billion has been taken out of the system since 2010, while LSE research has revealed that 500,000 people who would have got care in 2009 are no longer entitled to it, the alliance said.
CSA chairman Richard Hawkes said: "The message from GPs is clear - cuts to social care have directly led to extra pressure on primary care as well as huge challenges for hospitals.
"Chronic underfunding has left hundreds of thousands of older and disabled people, who need support to do the basics, like getting up or out of the house, cut out of the care system.
"As this polling shows, the impact is now being felt throughout the health service which is being forced to pick up the pieces.
"Ahead of next week's budget, we believe the Government needs to commit to serious investment in care, as well as in the health system.
"As health experts argue, anything else is a false economy."
The polling comes ahead of the Care Act coming into force on April 1 and as the Government is currently consulting on a cap on care costs.
Caroline Abrahams, charity director at Age UK, said: "This survey highlights just how bad a state the social care system is now in, and the hugely damaging knock-ons for older people's health and wellbeing as the pressures on GPs become more intense.
"We know that funding for social care has fallen dramatically and that without it older people are more likely to end up in their GP surgery or even in A&E because they have nowhere else to turn.
"This can't go on, we must fill the funding gap in social care if the NHS is to thrive."
Head of policy at the Alzheimer's Society, George McNamara, said: "Social services have been cut to the bone, increasing pressures on already stretched GP and hospital services.
"The situation is unsustainable and threatens to push thousands of vulnerable older people, many with dementia, into crisis.
"Political parties must stop treating social care as the poor relation of the better funded NHS.
"The government knows that reform and full integration is a necessity, but this can't be achieved on a shoe-string budget.
"We fully support the call for serious investment in care in the next budget."
Dr Maureen Baker, chairwoman of the Royal College of General Practitioners (RCGP), said: "GPs are facing unprecedented pressures in trying to care for increasing numbers of patients with increasingly limited resources.
"The RCGP strongly supports integrated services and we need to work in tandem with our colleagues in social care and wider community health teams to improve the long-term care that our patients receive."
A Department of Health spokeswoman said: "Social care is a priority for this Government. We have given an extra £1.1 billion to councils to help protect social care services this year on top of additional funding in recent years.
"GPs do a vital job and are at the centre of our plans as we move more care out of hospital closer to people's homes - our £5.3 billion Better Care Fund, the biggest ever national programme to join up health and social care, should improve care for thousands of vulnerable people, preventing 160,000 emergency admissions and saving over half a billion pounds next year alone."
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