A group of female school employees have won a Supreme Court victory in their equal pay fight against a local authority.

Five justices in London announced a ruling today in favour of 251 classroom assistants, support for learning assistants and nursery nurses employed by Dumfries and Galloway Council.

The issue in their appeal was whether they satisfied the threshold conditions set out under the Equal Pay Act 1970 to bring claims alleging that they are employed under less favourable terms and conditions than certain male employees of the council who do work of equal value.

The Supreme Court unanimously allowed their appeal and restored the decision of an employment tribunal permitting the claims to be brought.

It is now for the tribunal to decide whether the women's work is of equal value to the male "comparators" and, if so, whether there is an explanation other than the difference in sex for the difference between their terms and conditions.

The Unison union described the ruling as "historic" and said it was "worth millions of pounds for members".

Unison general secretary Dave Prentis said after the ruling: "I am delighted that the Supreme Court has ruled in favour of our women members.

"It is a shame, though, that they have had to go through this process and endure a seven-year wait just to get equal pay.

"Dumfries and Galloway Council should take immediate steps to correct their pay and I urge other councils to follow suit.

"We have more than 2,000 other cases on hold, waiting for this judgment.

"Employers should be in no doubt that this union will continue to pursue cases until all women are treated equally.

"There are far too many who are still discriminated against and far too many employers who are using every single legal argument and loophole to dodge their obligations under equal pay law."

Dumfries classroom assistant Karen Korus, one of the 251 appellants, said: "This has been a very long fight but we knew all along that we should be able to compare our work with the men, who sometimes did work in schools, but were not based there like us.

"I am so proud of the women here in Dumfries who stayed strong even when we lost a couple of decisions along the way.

"Unison has been fantastic and winning today will also help women in the future who want to compare themselves with men working from different places for the same employer."

Unison Scottish Secretary Mike Kirby congratulated the Dumfries women and said their success will immediately help nearly 2,000 members in Scotland with similar cases as well as having important wider implications.

He said: "This is a landmark case in equal pay across the UK. Unison's determination to fight for our members has successfully defended the intentions of the Equal Pay Act. Losing this would have been a serious setback for the Act itself.

"It is a disgrace that it is taking so long for women to get equal pay with men and that councils have fought to defend discriminatory practice in this way.

"More than 40 years after the Equal Pay Act, and after 30 years of equal value claims and 20 years after Scottish local authorities and trade unions reached agreement on implementing equal pay, there is finally no hiding place. It is time for councils to stump up and give our members what is due to them.

"It was always outrageous that any council employer should try to hide behind geography as an excuse for gender discrimination. The unions, the Scottish Parliament and the Scottish Government have been telling council leaders to get this sorted out.

"We are proud that it was Unison alone who got the final answer from the Supreme Court. We want to work now with Dumfries and Galloway Council and the other councils with outstanding cases to reach a speedy conclusion."

Dumfries and Galloway Council said in a statement: "This is a complex case, which has been considered by employment tribunal, Employment Appeal Tribunal, Court of Session, and now the Supreme Court.

"The Employment Appeal Tribunal and Court of Session both ruled in our favour.

"The Supreme Court judgment is the most recent stage of the legal process.

"The appellants, including classroom assistants and nursery nurses, now have won the right to have their jobs compared to those of male manual workers, such as road workers and groundsmen.

"This judgment has implications for many local authorities and other public bodies."

It said the council would "now consider its position in response to the Supreme Court judgment".

In bringing their equal pay claims, the women, who are employed during school term times only, had to establish that certain male employees are "in the same employment" as they are, even though they are employed on different terms and conditions and at different establishments.

Their claims were launched in 2006 and are primarily based on the allegation that their work is of "equal value" to that of the men.

The woman are employed at the council's schools under terms contained in a national collective agreement known as the "Blue Book", and want to compare their terms and conditions with those enjoyed by a variety of full-time manual workers employed by the authority as groundsmen, refuse collectors, refuse drivers and a swimming pool leisure attendant under a different collective agreement known as the "Green Book".

Those male workers are entitled to a substantial supplement on top of their basic pay - but the women are not.

In May 2008 an employment tribunal determined the "same employment" issue in the women's favour.

It ruled that they are in the same employment because they could show that if the male "comparators" were employed at their establishments they would be employed under broadly similar terms to those under which they are employed at present.

The employment appeal tribunal then allowed the council's challenge in 2009 and the Court of Session later held that the women failed on the evidence to show that if the men were to be based at schools they would be employed on Green Book terms and conditions.

Ruling in the women's favour today, Lady Hale, who has just been appointed as the new deputy president of the Supreme Court, said the employment tribunal judge "asked herself the right question and was entitled on the evidence to answer it the way she did".

Giving the background, Lady Hale said: "Under the Equal Pay Act 1970, women (or men) whose work is of equal value to that of men (or women) in the same employment are entitled to the benefit of a deemed equality clause in their contracts of employment.

"This means that if any of their terms and conditions is less favourable than the equivalent term or condition of the men with whom they are compared, they are entitled to have the benefit of that more favourable term, as if it had been included in their original contract of employment.

"It is therefore necessary to identify the precise terms and conditions with which comparison is to be made. This entails finding an individual or group of the opposite sex who constitute a valid comparator.

"There are several elements in that task. One involves looking at the kind of work the men and the women do: is it 'like', or has it been 'rated as equivalent', or is it 'of equal value'?

"Another involves looking to see whether there are material factors other than the difference in sex which explain the difference in treatment.

"But a threshold question is whether the men and women are 'in the same employment'. The issue in this case is what that means."

Lady Hale said the object of the legislation "is to secure equality of treatment, not only for the same work, but also for work rated as equivalent or assessed by the experts to be of equal value".

She said: "It stands to reason, therefore, that some very different jobs which are not or cannot be carried out in the same workplaces may nevertheless be rated as equivalent or assessed as having equal value."

Lady Hale pointed out that the fact that "of necessity" work has to be carried on in different places "is no barrier to equalising the terms on which it is done".

She added: "It is well known that those jobs which require physical strength have traditionally been better rewarded than those jobs which require dexterity.

"It is one of the objects of the equality legislation to iron out those traditional inequalities of reward where the work involved is of genuinely equal value."

For the "principle of equal pay to have direct effect, the difference in treatment must be attributable to a single source which is capable of putting it right".

Lady Hale said: "In this case it is quite clear that the difference in treatment between the claimants and their comparators is attributable to a single source, namely the local authority which employs them and which is in a position to put right the discrepancy if required to do so."

She said the "same employment" issue was "but the first hurdle which the claimants face".

After jumping that hurdle they "will still have to prove that their work is comparable to that of the men".

Lady Hale said: "Furthermore, if the claimants succeed in establishing that their work is of equal value, the employer could still seek to establish that there was a good reason for the difference between their terms and conditions."

Alastair Pringle, Scotland director for the Equality and Human Rights Commission, which intervened in the appeal, said: "The Supreme Court judgment confirms that Dumfries and Galloway Council's attempt to limit the circumstances in which women can compare their work and pay with that of their male colleagues is inconsistent with the fundamental right to equal pay for equal work.

"This case is another high-profile example of the significant amount of time it is taking women to pursue their claims for equal pay."

He said the decision "keeps the door open for thousands of other women who find themselves doing equal work as their male colleagues in the same employment, but who are paid less".

He added: "It also highlights the undervaluing of roles traditionally done by women and the practical impact of continued occupational segregation on women's pay."