More than 2,000 women making equal-pay claims against two of Scotland's largest local authorities will be in line for compensation worth thousands of pounds if legal action being brought on their behalf is successful.

The affected women made claims against North Lanarkshire Council and Glasgow City Council through the GMB union after a 2007 pay review designed to level the playing field between male and female staff was itself found to be discriminatory.

The GMB was accused of also discriminating against the women, however, because it only sought to have their pay re-rated for the period between 2007 and 2009. Fellow union Unison and claims firm Action 4 Equality Scotland based their own claims on the period from 2007 to 2012.

The GMB is now claiming that law firm Digby Brown - its sole Scottish legal adviser until 2015 - is to blame for the discrepancy and it is pursuing the firm in the Court of Session as a result.

It is understood that the union is seeking at least a six-figure sum from the firm and intends to pass on any money recovered if the action is successful to the affected women.

A spokesman for the GMB confirmed that the union has brought the action “in the interests of many members and former members”.

“GMB has commenced court proceedings against Digby Brown Solicitors in relation to advice given on equal-pay claims,” he said.

“Given this matter is presently in active litigation, it would be inappropriate to comment further.”

A spokesman for Digby Brown said that the firm was aware of the action and that “it will be getting defended”.

It is understood that the GMB has been preparing its case against Digby Brown since Gary Smith replaced Harry Donaldson as its regional secretary in September 2015.

A source close to the union said that when Mr Smith came on board “one of the first things he moved to do was ditch Digby Brown” because he felt “there had been poor advice around equal pay”.

In a letter sent to North Lanarkshire members shortly after taking over Mr Smith said he had launched “a full investigation into the North Lanarkshire case and a complete assessment of the legal strategy pursued by Digby Brown in relation to our equal pay cases in all of Scotland”.

The union parted company with Digby Brown soon after and now passes all its equal-pay work to Thompsons Solicitors.

North Lanarkshire Council - Scotland’s largest local authority after Glasgow City Council and the City of Edinburgh Council - has already paid out £130 million to settle equal-pay claims, which have come in two waves.

The first wave related to women missing out on bonuses paid to men they shared a pay grade with while the second came after those bonuses were amalgamated with male workers’ pay as part of the 2007 pay deal.

To date Glasgow City Council has paid out just over £90m to settle its own claims but that sum is expected to rocket after the local authority said it would negotiate second-wave claims rather than continue to oppose them in the courts. It has been estimated that Glasgow will have to pay between £500m and £1 billion to settle the dispute.

The GMB represents 2,000 Glasgow claimants and 200 in North Lanarkshire.