Costs to councils to cover social care for working age and lifelong disabled adults could top £17 billion by 2030, projections have suggested amid a warning the proposed National Care Service risks being an “empty slogan” without greater funding.

While this group makes up around 40% of all adult social care service users, almost two-thirds (63%) of council budgets went towards their care in the year to March, the County Councils Network (CCN) said.

Most of that 40% will be people aged under 65, the network said, although it also includes older people who have had a disability all their lives.

Costs of such care have risen sharply in recent years, the organisation said, driven by the complexity and type of care rather than more people needing support.

In analysis published by the network on Monday as the CCN’s annual conference took place, they projected the total increased cost to local authorities in England for this kind of care could rise by around half by 2030 to £17 billion.

Last year costs of providing care and support to working age adults and those with a lifelong disability is estimated to have been almost £11 billion, which the report says now “dwarf” the £6 billion spent on older adults with a physical disability and dementia.

The analysis, with consultancy firm Newton, was based on publicly available national data alongside local input from 16 local authorities to project future costs and excluded council staffing and administration costs.

It indicated that 18–24-year-olds currently account for around 13% of current expenditure on working age and lifelong disabled adults, which equates to around £1.4 billion a year.

The report stated that there is an expectation spending on support for this age group will grow by at least 40% by 2030 “as a consequence of increases in Send (special educational needs and disabilities) and population growth”.

Martin Tett, CCN spokesperson for adult social care, said: “Caring for working age and lifelong disabled adults is one of the most important and rewarding responsibilities councils carry out.

“But too often in the debate on adult social care their needs and challenges are forgotten.

“Our research reveals that far too many working age and lifelong disabled adults are placed in expensive and sometimes inappropriate residential placements.

“This is bad for councils and even worse for care users who see their independence drastically reduced.

“For individuals and councils, the National Care Service risks being an empty slogan unless it is backed with a renewed focus on working age adults, and significant increase in funding for councils to meet rising costs and ensure the quality and safety of support is maintained.”

Jackie O’Sullivan, executive director of strategy and influence at learning disability charity Mencap, said described the financial “worrying” and said it “reinforces our concern about the growing demand for adult social care and the lack of funding and suitable provision available to people who need it most”.

She added: “We are now seeing an alarmingly large number of young people transitioning to adulthood without the support they need to live independently and play a full part in their communities and society at large.

“We simply cannot allow that to happen.

“The report highlights that you can’t fix social care without working age and disabled adults being at the heart of creating a National Care Service.”

The Local Government Association (LGA) also described the projections as “concerning”, noting that while the sector is “often seen primarily as a service for older people” when in reality many people needing such care are younger, working-age adults with disabilities.

David Fothergill, chairman of the LGA’s community wellbeing board said: “While their aspirations, such as independence, relationships, and hobbies, may align with those of older generations, supporting them effectively requires a distinct approach.

“This report highlights the urgent need for focused attention on this group as we address funding and reform.”

A Government spokesperson said: “We have inherited a broken social care system and will work closely with the sector to build a National Care Service that will improve the quality of care for working-age disabled adults across the country.

“The Chancellor has announced at least £600 million of new social care funding, as well as an £86 million increase for the Disabled Facilities Grant, which are part of a wider package to bolster support for councils.

“We are also committed to reforming Jobcentres to provide better employment support and make health-related benefits more flexible, making it easier for people to move into paid work.”