The average amount of savings accumulated in a Care Isa would not be enough to pay for residential care in later life, research from Just Group has suggested.
The research found the average stay in a care home was 130 weeks but the amount of savings accumulated in the average Care Isa would not be enough to cover this cost.
The Care Isa is a proposal reportedly being considered by the Government as part of its forthcoming green paper on social care, due to be published in the autumn.
It would consist of a savings pot exempt from inheritance tax to fund social care in later life.
But even with inheritance tax exemption, Just calculated people would still struggle to afford late life care.
Stephen Lowe, group communications director at Just Group, said: "Isas have been a popular way for people to save tax-efficiently for nearly 20 years but even over that timescale the average holder has not built up enough to pay for even a single year of care.
"With more than half of 45 to 54-year-olds telling us they haven’t even thought about paying for care, it’s difficult to imagine how a new Care Isa could suddenly spark the dramatic shift in savings that will be needed to meet these potentially huge residential care bills in the future."
According to Just's research, the average Isa value in the north east was £19,915, enough to pay for only 35 weeks of care.
Meanwhile the north west had an average Isa size of £21,560 which could pay for 41 weeks' care.
In London the average Isa value was among the highest in the country at £25,982 but high care costs in the capital meant the money would only last 36 weeks.
Mr Lowe said: "Only about four in 10 of the adult population has an Isa, falling to three in 10 in Northern Ireland. Fewer than one in 20 estates are taxed on death so the appeal of a tax break is limited.
"While most people have relatively modest care costs, the biggest problem is the minority who end up needing care for many years but cannot hope to save the six-figure sums to pay for it themselves.
"Government proposals would be better focusing in the short-term on how to incentivise people aged 50 and over to use some of the many trillions tied up in their properties to support their later life care costs and focus longer-term policy development on establishing solutions to pool risk so people can be protected from catastrophic care costs that destroy their life savings."
When asked how they would like to pay for social care was, just a quarter of UK adults said they would choose the Care Isa.
Kay Ingram, director of public policy at LEBC, said: "The concept of a Care Isa is flawed and is unlikely to result in enough being saved to meet care costs.
"Only one in four older people currently need social care. Saving for this specific purpose is unlikely to be attractive, as most people will not need care and would be better off saving for their general needs in retirement. They can more easily do so with pension savings , which allow those who don’t need care to spend the money on other things or left tax free on death to loved ones.