One in 10 councils have cut their spending on social care by more than a quarter, a respected economic think tank has found.
The Institute for Fiscal Studies (IFS) found that overall local authority spending on social care fell by 11% in real terms between 2009/10 and 2015/16.
Their research also shows that six in every seven councils has made at least some cut in its care spending per adult resident over this timeframe.
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.
"The spending cuts analysed in our report have been accompanied by a substantial fall in the number of people receiving social care: down 25% across England, between 2009/10 and 2013/14 alone," said Polly Simpson, a research economist at the IFS and an author of the report.
"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% - and metropolitan districts such as Greater Manchester, Merseyside and Tyneside.
The North East also saw a drop of 18% 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.
Spending fell below £325 per adult resident in a tenth of council areas, while it was 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.
Labour care spokeswoman Barbara Keeley described the report as a "damning verdict" on Government cuts totalling £4.6 billion between 2010 and 2015.
"It's essential that the Government green paper on future funding for social care puts forward solutions to solve the current crisis but also sets out a fair, long-term, sustainable funding solution so that those who need social care, whether they be older people or adults with complex needs, get the support they deserve," said Ms Keeley.
A Government spokesman 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.
"It's also why we're committed to having a fair and more sustainable way of funding adult social care for the future, especially given people are living longer. We'll be setting out our proposals in a forthcoming green paper."
However, Margaret Willcox, president elect of the Association of Directors of Adult Social Services (ADASS), said the extra £2 billion was "only a short-term measure".
Linda Thomas, vice-chairwoman of the Local Government Association's Community Wellbeing Board, added that the report " reflects the historic and chronic underfunding of adult social care by successive governments".