The Co-op’s former HR director Sam Walker has brought a lawsuit against the retailer on the grounds of unequal pay, discrimination and unfair dismissal.

Walker, who acted as chief HR director for The Co-operative Group from February 2014 until April 2016, will have her case against the firm heard at an employment tribunal in Manchester over the next two weeks.

The grocer’s former director claims that she first raised concerns about the pay disparity between herself and fellow male board members in 2015.

In her witness statement today Walker claimed that some board members were offered large salaries in 2013-14 while the firm was “in crisis” in a bid to stop them leaving the group.

Walker said that in 2014 pay rises were agreed with former general counsel Alistair Asher and chief external affairs officer Nick Folland, both of whom were paid £550,000, while she and former chief strategy planning officer Paula Kerrigan were offered £400,000, “ostensibly because we were newly promoted to our roles”.

According to Walker’s lawyers, an independent assessement of the Co-op’s executive roles by the Hay Group in January 2015 rated Walker’s former role higher than Asher and Folland’s, while Kerrigan’s was higher than Folland’s and on par with Asher’s.

According to The Guardian, Walker said she was “not treated equally in terms of pay with two male colleagues in the Co-op’s executive team and that I was victimised and discriminated (and ultimately dismissed) when I raised concerns about this”.

Walker added that she flagged to The Co-op’s former chief executive Richard Pennycook that women in general appeared to earn less than men across the group following a company-wide grading structure in 2016.

“I told him that I thought the Co-op had an equal pay problem which not only exposed the business to legal claims, but was inconsistent with the Co-op’s declared values,” she said.

Walker said that she suggested she be offered more holiday to ensure her “pro-rated pay could be equivalent to the men on the executive committee” but was instead told she had to accept a new and reduced role in the firm.

“The only reason I could think I was being treated in this way was because I had dared to raise the issue of equal pay,” she said.

A spokesman for the Co-op said: “We do not accept that Sam Walker was discriminated against or treated detrimentally, and intend to fully and robustly defend the various claims brought by Sam.”

The grocer’s lawyer Andrew Burns argued that Walker’s performance in her role was questioned over the progress of a significant IT project she spearheaded called 1HR, which was described as “over time and over budget”.