The region's 12 successor authorities were appealing against the decision of an industrial tribunal to back the instructors' equal-pay case, one of a string that could cost west of Scotland councils millions of pounds in back pay.
Rod McKenzie of Harper MacLeod, solicitor for eight instructors who launched the test case more than three years ago, said his clients were being paid "massively less" for work Strathclyde acknowledged was the same as that carried out by teachers.
"From the employers' view, it did not seem to matter that staff were not teachers or GTC (General Teaching Council) registered," Mr McKenzie told the tribunal chaired by Lord Johnston.
In practice, despite the different training and qualifications, instructors did the same work. Teachers did not have more responsibility.
Mr McKenzie said teachers were paid the rate for the job but he could not understand why instructors were not. All the Equal Pay Act required people to do was prove that a man or woman was being paid more than someone doing similar work. "This case was not brought as a fair wages case. It's a case brought by the applicants under the Equal Pay Act. If, as a consequence, they end up with fair wages, good luck to them," Mr McKenzie said.
He dismissed suggestions that paying the instructors more would lead to a "meltdown" in the structure of APTC staff, the local government scale on which they are currently paid.
Ian Truscott, counsel for the local authorities, insisted Strathclyde had no obligation to pay people the same even if they were doing the same work.There was also no argument that instructors and teachers were doing similar jobs.
He accepted the employers' position was "not entirely fair" but the instructors' case was more a matter of industrial relations and regrading than eliminating sex discrimination under the equal pay legislation.
There was nothing in law to force Strathclyd e to match teachers' pay. There was no fair wages act and the industrial tribunal was telling the council how to spend its money, he said.
Interrupting Mr Truscott's submission, Lord Johnston asked: "How can it be sex discrimination when it's between instructors and teachers?".
Mr Truscott replied: "I would encourage you to maintain that difficulty." The industrial tribunal was wrong to back the instructors on several counts, including its interpretatio n of the Equal Pay Act, he said. The tribunal was "grossly unfair" to Strathclyd e when there was no sex discrimination.
Mr Truscott argued that the tribunal also disregarded the important knock-on effects on the council's budget if instructors had been paid more.He re-emphasised that a further 114 cases had been lodged with the industrial tribunals.
"The difference in pay is so great that the destabilising effect within the APTC scales would be considerable. The maintenance of differentials is a very real one," he said.
He added that Strathclyde was compelled to pay teachers a certain rate because of statutory obligations under the Scottish Joint Negotiating Committee but there was no such ruling governing instructors. "Having listened to the women, if possible I would have found the money to pay them more," he continued.
However, Strathclyde did not have the money and was not forced to pay them under current legislation, he said. Lord Johnston reserved judgment.