The bloc’s top court indicated that pay conditions for shop-floor workers can be compared with the company’s distribution staff.

It said the legal test for comparability is one of three tests involved in the case, which could take years to conclude.

A Tesco spokesperson said: “The jobs in our stores and distribution centres are different.

“These roles require different skills and demands which lead to variations in pay – but this has absolutely nothing to do with gender.

“We reward our colleagues fairly for the jobs they do and work hard to ensure that the pay and benefits we offer are fair, competitive and sustainable.

“These claims are extremely complex and will take many years to reach a conclusion. We continue to strongly defend these claims.”

Law firm Leigh Day represents more than 50,000 supermarket shop-floor workers, most of whom are women, who claim they are paid unfairly in comparison with distribution centre colleagues, most of whom are men.

Kiran Daurka, a partner at the firm, said: “This judgment reinforces the Supreme Court’s ruling that the roles of shop-floor workers can be compared to those of their colleagues in distribution centres for the purposes of equal pay.

“For a long time, employers have argued that UK law in this area is unclear, but this judgment is simple: if there is a single body responsible for ensuring equality, the roles are comparable.

“Clarification from the CJEU confirms that this single-source test can be relied upon by people in the UK bringing an equal-value claim.

“This means that employers can no longer hide behind the grey areas of UK law.”