More than 150,000 people have signed a petition calling for urgent action to fix the system that provides care for older and disabled people.
It urges the prime minister "to end swingeing cuts", saying more than 1.4 million over-65s in England have been left without the support they need.
Also, 40 health leaders have written to Boris Johnson to warn adult social care cuts have a knock-on effect on the NHS.
Government says real-terms funding is rising by 8% from 2015-16 to 2019-20.
Last month, on his first day as prime minister, Mr Johnson said: "I am announcing now - on the steps of Downing Street - that we will fix the crisis in social care once and for all with a clear plan we have prepared to give every older person the dignity and security they deserve."
But the letter calls for:
- a plan with cross-party involvement
- a long-term financial settlement
- short-term money to shore up services this year
- support for a wider range of people
One of the signatories, Sussex Community NHS Foundation Trust chief executive Siobhan Melia says vulnerable people are facing unacceptable delays in accessing the care that they need "due to a dearth of provision of social care packages.
"This means that NHS teams are caring for people longer than they need to, placing increased demand on community and hospital services."
It's 12:00 and 79-year-old Edna Clark's lunch has just arrived at her home in Bishop's Stortford, Hertfordshire.
It's chicken curry, her favourite, and she's tucking in with gusto but she looks forward to all the food provided by the meals-on-wheels service.
This help started after a four-month stay in hospital, during which, because she had been so ill and wasn't eating properly, her weight dropped from nine stone to about five.
Being partially sighted means preparing food is difficult for Edna.
"I couldn't see the gas ring - and if I used the front one, I could have crossed over and burnt myself or set my clothes on fire," she says.
The service has not only helped her get back to a healthy weight but she also enjoys chatting with the people who deliver the food and they keep a check on her.
Unfortunately, the squeeze on council finances over the past decade means many can no longer afford this sort of early intervention scheme.
Sarah Wren, who runs Hertfordshire Independent Living Service, providing meals on wheels as well as exercise and nutrition advice, says an ageing population means this kind of investment in prevention is crucial.
"We have to give this support to people at home if we are going to make inroads into saving the money the NHS is going to keep needing," she says.
But the financial uncertainty faced by Hertfordshire County Council and other local authorities means tough financial decisions ahead.
The county's director of adult social services, Iain MacBeath, pays for these preventative services through short-term government grants and doesn't know if the money will continue beyond next March.
"It's very painful for me to have to consider reducing their funding or even cutting services," he says.
"I really believe that every pound we spend on meals on wheels saves something down the line.
"It's just if we are forced into a position where we can't wait for down the line, it means being penny-wise and pound-foolish."
Adult social care is the support provided for older and disabled people in their own homes or in residential and nursing homes.
Care workers help people with day-to-day tasks such as washing, dressing, eating and taking medication and this regular contact reduces loneliness, helps spot problems early and keeps people out of hospital.
With more people living longer and with more complex conditions, demand for social care is increasing.
At the same time, local authorities have seen the money they receive from central government drop significantly in the past decade.
The Local Government Association, which represents councils in England, puts this year's funding shortfall at £2.5bn.
The letter and petition have been organised by the NHS Confederation, which leads the Health for Care Alliance of 15 national health organisations.
"This is a crisis and it has to be urgently addressed," says NHS Confederation chief executive Niall Dickson.
"As our petition shows, the public recognise the human cost of inaction and they want this resolved.
"Successive governments have failed to address this issue - the new government has a chance to put this right."
A Department of Health and Social Care official said: "The prime minister has been clear he is committed to fixing the social care system and will outline proposals as soon as possible.
"We have given local authorities access to nearly £4bn more dedicated funding for adult social care this year and a further £410m is available for adults and children's services."