Four out of five local councils say they do not have enough capacity to care for older people in their area, a study suggests.
The report, from the Family and Childcare Trust, included Freedom of Information data from around 150 local authorities and health and social care trusts across the UK.
It showed shortages in key areas, including providing care to elderly people in their own homes.
While 84% of local authorities in the UK had enough availability for care home places, that figure fell to 48% for providing care at home.
And only a third (32%) of local authorities said they had enough nursing homes with specialist dementia support.
The figures also varied by region, with 57% of councils in the North East having enough older people's care to meet demand in their area, dropping to just 7% in outer London.
Claire Harding, head of research at the Family and Childcare Trust, said: "It is inexcusable that vulnerable people are left unable to find the care that they need.
"We urge the Government to make sure there is enough care for everyone who needs it. In order to do this, we need robust data on where there are gaps in care, a funding system that truly meets the cost of providing care, and clear information for families.
"Without these steps, families will continue to struggle to find care and to meet the numerous care costs on their shoulders."
The study was funded by Legal and General.
Earlier this month, the Local Government Association (LGA), which represents councils, said money is being diverted away from road repairs, leisure centres and local bus routes in order to maintain the struggling social care sector.
It warned that the system is "in crisis" and called on the Government to invest in social care in the Autumn Statement.
The LGA said that councils spend around 35% of their budgets on adult social care and are increasingly having to divert money away from other services to plug gaps.
It said adult social care services face a potential funding gap of at least £2.6 billion.
A Department of Health spokeswoman said: "This Government is committed to making sure older people throughout the country get affordable and dignified care.
"That is why we are significantly increasing the amount of money local authorities have access to for social care, by up to £3.5 billion by 2020."