Judges at the UK's highest court have dismissed a profoundly disabled man's appeal over his care package.
Lawyers representing 26-year-old KM, who was born without eyes and has a range of serious mental and physical conditions, said the case raised "profound issues" for disabled people dependent on local authority support.
They told the Supreme Court that Cambridgeshire County Council made an "irrational" decision when funding his care.
They said the council's offer of around £85,000 a year was "manifestly insufficient" to meet the man's "assessed eligible needs" - and told seven justices that an independent social worker put the cost of an annual support package at £157,000.
But today the judges unanimously rejected the challenge to the rationality of the local authority's decision in relation to KM, who cannot be identified for legal reasons.
Lawyers at Irwin Mitchell, which represented four charities intervening in the case - Sense, The National Autistic Society, The Royal National Institute of Blind People and The Guide Dogs for the Blind Association - said that the landmark judgment clarified social care law.
Although KM lost, the ruling made it clear that local authority resources were not to be taken into account when establishing the needs of disabled people.
Some councils restricted assessments on the grounds of costs and some did not, which in the past resulted in a postcode lottery for social care.
Importantly, the court also made it clear that when social care support was provided by direct payments to the individual it was "crucial" that local authorities provided a reasonable degree of detail so that a judgment could be made whether the indicative sum was too high, too low or about right.
Partner Yogi Amin said: "This is potentially the biggest community care ruling in 15 years.
"Although KM's appeal has not been successful, we are pleased that the Supreme Court has now clarified the law with regard to local authorities taking their resources into account when assessing a disabled person's needs."
Richard Leaman, chief executive of Guide Dogs, said that, while sympathising with KM and his family, they were delighted that the case has removed any ambiguity regarding the point at which a local authority was entitled to take its resources into account.
"We have consistently argued that a person has the right to a full assessment of their needs, regardless of whether a council is subsequently obliged to meet them."
Simon Foster, head of legal services at Sense, said: "We are delighted that the court has made it very clear that a local authority must assess disabled people in the first instance based on their needs, rather than what is available in the local authority's budget.
"We believe in the principle that a person's needs ought to be assessed in full, without regard to financial considerations. We are also pleased to see the court confirm that a local authority must give sufficient detail when providing direct payments so disabled people can see if the amount is enough to meet their needs."
Mark Lever, chief executive of The National Autistic Society, said that the fact that the court recognised that assessment for social care should not be based on a "computer says so" system was an important step forward.
"This sends a clear message to all local authorities that they have a duty of care to be transparent about how they assess and allocate funds to disabled people whether they live in Liverpool or Luton.
"The case highlights the complexity of the current social care system and the need for the Government to stop delaying in their reforms and put an end to the care crisis."