Thousands of women who fought Glasgow City Council for equal pay have had money deducted from their compensation packets to cover legal fees after unions entered into a secretive deal before negotiations began, a new investigation has revealed.

Members of Unison, Unite and the GMB were told they would receive the full amount of settlement money offered by the local authority after a long-running dispute over a disparity in pay between male and female workers was resolved in January.

However, according to documents seen by the BBC, all claimants have had fees deducted from the £548 million compensation pot designed to redress the balance after ‘equal pay specialists’ Action 4 Equality agreed a 6.9 per cent contribution would be taken from each of the 16,000 women it represented.

The council agreed to pay out after a job evaluation scheme adopted in 2007 saw ‘traditionally female-dominated’ roles such as catering or home care paid up to £3 per hour less than ‘male-dominated’ jobs such as refuse workers or gardeners.

READ MORE: Glasgow's equal pay fight settled in deal worth £548m

Under the terms of the settlement, none of the women were allowed to speak about how much they were awarded, but the BBC understands they were also not informed that fees would be applied to their package.

Each woman had an "individual offer" depending on how far back they were allowed to claim, how much they were underpaid per hour and how many hours they worked – but were not told how the amount was calculated.

Most of the claimants were represented by Action 4 Equality, operated by lawyer Stefan Cross.

But employment lawyer Carol Fox, who worked with Mr Cross on the Glasgow case between 2008 and 2015, told the Disclosure programme that unions only began to put claims in for the women when they saw the success of other companies who were taking on councils and winning.

Ms Fox, who also worked on equal pay cases in North and South Lanarkshire, told the programme she was "troubled" by aspects of the settlement.

She left the company in 2015 and played no part in the final negotiations for the Glasgow settlement.

"That deal is very different from all the other settlements that we reached," she said. 

"It doesn't appear to me that the women have been told the detail of what they've paid. And who they've paid it to, and what it's been for."

All the unions had promised members they would get all the money they were owed.  

By the time of the Glasgow settlement, Unison had dealt with 5,000 claims, while the GMB had more than 2,500 and Unite had a small number of claims.

However, Disclosure revealed the three unions - as well as Action 4 Equality - entered into a deal before negotiations began with the council. 

As part of this deal, it was agreed that every claimant would have a percentage of the settlement offered by the council deducted in legal fees - including those backed by their unions.

All of the claimant organisations told the programme their members or clients benefitted from this deal and received higher offers by working together.

But Audrey Masson, a home carer represented by the GMB, said: "Nothing against Stefan Cross, why should we have to pay, because I never signed for him to represent me. I signed for the unions."

Mr Cross, the director of Action 4 Equality, said that by signing their settlement offers, claimants agreed to the terms.

READ MORE: Equal pay battle could have cost a fraction of £550m bill

He said: "Every single agreement includes a legal commitment to make that payment."

The unions said settlements were based on a "complex formula" and they could not discuss them because they were confidential.

As well as the legal fees, Disclosure also discovered that potentially thousands of workers have missed out on claiming for the full extent of their discrimination.

Under Scottish law, workers who have been discriminated against are entitled to five years back-pay if their case is successful.

However, because the pay dispute at Glasgow City Council has gone on since 2006, the maximum time period claimants can receive compensation for is 12 years.

Audrey Masson worked as a home carer for 15 years but is receiving only five years back-pay, but alleges her union never told her to put in a claim.

She did eventually lodge a claim but too late to receive the full amount of 12 years of back-pay.

Ms Masson said: "We stood on the picket lines for equality, and we didn't even get it. Most of the people that stood on the picket lines didn't even know they were only getting five years."

The GMB union, who represented Ms Masson, denied claims were put in late.

In an interview with the BBC, Gary Smith, GMB Scotland Secretary, said: "We were given the wrong legal advice, we did not pursue the same cases as the private lawyers, or indeed one of the other unions. But our members were not left at a detriment in the end."

Disclosure: The Great Equal Pay Scandal airs tonight at 8.30 pm on BBC One Scotland.