The number of people aged 85 and over needing 24-hour care is set to double, says a new study, as an expert warns the care system is "at breaking point".
The study, published in the Lancet Public Health journal, analysed the projected health needs of the elderly between 2015 and 2035.
It found that the number of 65-year-olds and over needing round-the-clock care is also set to rise by a third.
The government says adult social care reforms will be set out in the autumn.
The modelling study, carried out by Newcastle University and the London School of Economics and Political Science, highlighted the fact that the fastest growing demographic in the UK is elderly people over 85, whose numbers are projected to more than double by 2035, increasing by 1.5 million.
Many of these elderly will develop multiple long term health conditions, with increasingly complex care needs.
Prof Carol Jagger, from the Newcastle University Institute for Ageing and senior author of the study, said the number of unpaid carers is in decline.
She warned that relying on unpaid family carers was not sustainable and said: "The challenge is considerable. Our study suggests that older spouse carers are increasingly likely to be living with disabilities themselves.
"On top of that, extending the retirement age of the UK population is likely to further reduce the informal carer pool, who have traditionally provided for older family members. "
Nick Forbes, senior vice-chair of the Local Government Association, warned that more investment was needed to avoid a crisis.
"Adult social care services face a £3.5bn funding gap by 2025, just to maintain existing standards of care," he said. "The system is at breaking point, ramping up pressures on unpaid carers.
"There is an urgent need to plug the immediate funding gap and find a long-term solution to how we pay for adult social care."
The study also noted that there were increasing numbers of adults aged over 65 living independently, with a rise of 60% forecast by 2035.
However, as they got older men were more likely to remain independent, whereas women will spend almost half of their remaining life with low dependency needs and more years needing intensive 24-hour care.
Prof Jagger said: "Trends for men and women are likely to be very different, with women experiencing more low level dependency than men, highlighting the importance of focusing on disabling long-term conditions, such as arthritis, that are more common in women than men.
"The rise in obesity is hitting women harder than men, and men have probably benefitted more from the reductions in cardiovascular disease. Women also suffer from a decline in muscle mass and so I am stressing the importance of physical activity and maintaining strength and balance."
Prof Jagger added: "This expanding group will have more complex care needs that are unlikely to be met adequately without improved co-ordination between different specialities."
Ageing population 'challenge'
The report comes as the government is considering how to reform social care.
In June, a funding rise was agreed for the NHS, in which its budget will increase by £20bn a year by 2023.
A Department of Health and Social Care spokesperson said: "In the autumn we will set out our plans to reform adult social care alongside our long-term plan for the NHS, so we can address the challenge of our growing ageing population head on and ensure services are sustainable for the future."
Caroline Abrahams, charity director at Age UK, urged the government to meet the challenge head on and stressed that the burden on families is too great.
"The problem is that today there are far too few really effective joined-up services and social care is in sharp decline," she said.
"The government's top priority must be to steady the ship and then produce a great set of proposals later this year to give our older population confidence they can get the help they need."
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