The conclusion of the longest employment tribunal wrangle in Scottish legal history means the councils have now saved around pound;161 million by contesting and winning a raft of equal pay cases over the past decade.

Virtually all regrading cases involved women who argued they were being paid less than men, but judges have consistently ruled their pay was lower for reasons other than their sex.

The latest judgment on eight instructors from the former Strathclyde Region confirms that view. They took their self-financed case to the Lords with assistance from Glasgow solicitors Harper Macleod, after two victories in employment tribunals were overturned by the Court of Session in Edinburgh. The case began more than six years ago.

The authorities accepted the instructors were doing identical work to teachers in special schools, although they were paid up to pound;10,000 less. However, te councils argued successfully that if institutions were called schools they had to be staffed by qualified teachers, whose pay was determined by the statute of the Scottish Joint Negotiating Committee. It did not matter that the instructors may have had a just case.

Lord Slynn of Hadley comments: “This is plainly in essence a claim that the pay is not fair - and not a claim that the pay is unequal because of discrimination between the sexes. As such it does not fall within the Equal Pay Act 1970.”

Ironically, it was the statutory protection of the SJNC that saved councils from paying out millions in compensation. A voluntary collective bargaining agreement would not have offered the same guarantees, an adviser said.

Rod McKenzie, the instructors’ solicitor, warned the councils that the Lords judgment still left the door open for yet another legal challenge over indirect sex discrimination. Harper Macleod would be able to choose from one of a further 139 instructors, whose claims have been suspended during the test cases.