Personal care support for more than 9000 elderly Scots was thrown into doubt by a legal ruling which yesterday sharply criticised SNP ministers for refusing to explain the flagship policy in court.

Lord Macphail published a ruling that rips a hole in the free personal care policy, finding that more than £70m is being spent by councils each year without proper legal backing.

His judgment removes the requirement on local authorities to pay the £145 weekly grant for personal care to those who fund their own room and board in residential care homes. The most recent figures suggest that covers around 9500 pensioners, mostly with more affluent backgrounds.

The Scottish Government's refusal to respond to the judge's request to explain the policy was criticised by the SNP's opponents. LibDem Ross Finnie said it was "an astonishing dereliction of duty", Labour's Wendy Alexander accused Nationalists of being too busy picking fights with London, while Mary Scanlon, for the Conservatives, said uncertainty must be removed.

The finding puts pressure on the government to clarify free-care legislation, which has caused confusion on several fronts in the five years since it was introduced.

Yesterday's ruling was on a legal dispute over a local authority's legal responsibility to provide free personal care. It arose over the case of William McLachlan who lived in Helensburgh and last year waited three months between being assessed as needing personal care and receiving payments for it from Argyll and Bute Council. Mr McLachlan died in April this year, aged 91. His son, also William McLachlan and living in Helensburgh, had taken up the case with the Public Services Ombudsman, Alice Brown.

She ruled last November against the council for delaying payment once Mr McLachlan had been assessed as needing free personal care, and then for refusing to backdate payments once they began. The council challenged her ruling by seeking judicial review in the Court of Session.

After the three-day hearing earlier this year, Lord Macphail's ruling yesterday used strong language, by legal standards, to criticise the government for snubbing his request to explain its policy in court. It had responded that it was not party to the legal dispute and it was up to the courts to interpret the law.

The judge said ministers' reasoning was "trite", that they failed to understand the terms under which he asked them to appear, and that it would have been in the public interest for the government to explain its position.

He said he reached his judgment "with reluctance", recognising that the matter is one of "great public interest which affects very many people".

However, he concluded the language in the Community Care and Health (Scotland) Act 2002 was "unambiguous". He said: "It is not possible to interpret it as obliging a local authority to make payments for social care which is not provided by them."

Health Secretary Nicola Sturgeon yesterday appeared to contradict the judge's ruling: "We do not believe this ruling has any implications for the current operation of the policy.

"The ruling reflects how the policy is operating and was intended to operate - people are entitled to free personal and nursing care following a care-needs assessment and once a local authority care contract is in place.

"This applies to people who arrange their own care and people who have their care organised by a local authority."