One in 10 councils have cut their spending on social care by more than a quarter, a think tank has found, prompting warnings from campaigners that the system is "no longer able to cope with increasing demand".

Overall local authority spending on social care fell by 11 per cent in real terms between 2009/10 and 2015/16, with six in every seven councils having made at least some cut in its care spending per adult resident over the period, the Institute for Fiscal Studies (IFS) found.

The findings add to growing concerns about the long term sustainability of social care, though ministers insist councils will have access to billions of pounds of extra funding over this Parliament.

It comes after it emerged last week that nearly half of care workers leave the job within a year, with seven per cent of roles (84,000 jobs) vacant, pointing to “severe challenges in maintaining staffing levels”, amid warnings that another 275,000 people will be needed to work in the sector by 2025.

Polly Simpson, a research economist at the IFS and an author of the report, said: “The spending cuts analysed in our report have been accompanied by a substantial fall in the number of people receiving social care: down 25 per cent across England, between 2009/10 and 2013/14 alone.

“Cuts have therefore been delivered, in part, by removing care from many people, with those still receiving care presumably those with the highest needs.

“What all this means for the quality of care received, the welfare of those no longer receiving care, and other services like the NHS, requires further research to answer.”

Spending fell by most on average in London - 18 per cent - and metropolitan districts such as Greater Manchester, Merseyside and Tyneside, while the North East also saw a drop of 18 per cent in social care across the region.

The IFS research, funded by the Health Foundation, found major variations in what individual councils spend on social care, with spending falling below £325 per adult resident in a tenth of council areas, while standing at more than around £445 in another tenth of authorities last year.

In terms of regions, councils in East Anglia, the North East and South West spent just short of £400 per adult resident, compared to around £360 for the lowest spending regions in Yorkshire and the Midlands.

David Phillips, an associate director at the IFS and another author of the report, said: “One thing that stands out in these figures are the big differences in spending per adult on social care among councils assessed to have very similar spending needs by the Government.

“Whether this means spending needs assessments are inaccurate, or reflects differences in available funding or the priority placed on social care relative to other services or council tax levels, is unclear.

“But it emphasises that the Government has got its work cut out in its 'fair funding review' of how to measure different councils' spending needs from 2019 onwards. That debate could get quite fraught.”

Responding to the findings, Genevieve Edwards, Director of External Affairs at the MS Society, said: “A sustainable solution is desperately needed to reverse the damage already done to our social care system by years of chronic under-funding.

"Today, one in three people with MS with the highest needs aren’t getting basic help with things like washing, dressing and eating. Rising numbers of people with MS are now having to fund their own care to help them manage this unpredictable and challenging condition.

”The £2 billion announced in last month's Budget will provide short-term relief. But without long-term funding, older and disabled people, families and carers, and the NHS will continue to pay the price for a system no longer able to cope with increasing demand.”

A Government spokesperson said: “We recognise the challenges councils face in delivering social care and the need for a long-term sustainable solution. That's why we're giving councils an extra £2 billion to help deliver these services, taking the total to an additional £9.25 billion over the remainder of this Parliament.