The future of free personal care for the elderly is in doubt after a judge ruled that councils are not obliged to meet the costs of pensioners who arrange their own care in private nursing homes.

In a landmark case, Lord Macphail said the law could not be interpreted to mean councils have to pay for social care they had played no part in securing. But he described the elderly care legislation as “ambiguous” and “unusually complex”.

Argyll and Bute Council, which sought judicial review after the Scottish Public Services Ombudsman said the council had failed to provide a statutory service to an elderly man, welcomed the finding.

“The decision by Lord Macphail is lengthy, and the council is now taking time to consider the findings fully,” said a spokesman.

Conservative MSP Mary Scanlon, shadow cabinet secretary for health and wellbeing, said the ruling was “deeply concerning” and had brought uncertainty to elderly people in private homes and their families.

She accused ministers of letting elderly people down by failing to cooperate with the court in order to clarify the purpose of the legislation. “It is very concerning that the SNP government, so quick to criticise Westminster for non-co-operation with the Scottish Parliament, refused to instruct counsel to appear before the court on a matter of this importance,” she said.