Employment lawyers Leigh Day are representing 400 mainly female workers in an equal pay case against Asda that could end up costing Britain’s supermarkets millions of pounds in in higher wages and back pay.

The Asda case revolves around determining if supermarket store jobs, which are mainly held by women, are of equal value to higher-paid jobs in the distribution centres, jobs which are mainly held by men.

If successful, the workers could be entitled to six years back pay for the difference in wages. It will also have major implications for the rest of Britain’s supermarkets, particularly if they own their own distribution centres, as many do. “The implications for any supermarket are enormous,” said Michael Newman of Leigh Day, the firm representing the workers.

Michael Newman went on to say: “In the supermarkets check-out staff and shelf-stackers are mostly women. The people in the warehouses are pretty much all men. And, who would be surprised, the group that is mostly men gets paid more,” he said. “We are very confident that the jobs are pretty much the same. In the warehouses they take stuff off the shelves, put it on a pallet and stick it on a lorry. In the supermarket, they do the reverse: take the pallets off the lorry, unstack them and put stuff on the shelves.”

Asda said in a statement: “We are aware of a small number of claims. We pay a fair market rate for the job people do regardless of gender and we don’t recognise discrimination in our business.”

Victory would mark a significant step in the battle for equal pay, said Newman. “There has been huge advancement in the public sector. But in the private sector it is still the 1970s. Job evaluations don’t happen. Cases aren’t brought. So you still get this very segregated workplace. Women are over here doing the women’s work and men are over there doing men’s work.”

The case will be heard at Manchester Employment Tribunal within the next two months.