Asda store workers have won a Supreme Court equal pay fight with supermarket bosses.

More than 40,000 Asda store workers, about two-thirds of whom are women, brought equal pay claims saying staff working in distribution depots, most of whom are men, unfairly get more money.

Asda bosses said store jobs are not comparable to distribution centre jobs.

Supreme Court justices on Friday ruled in favour of the store workers.

They decided they were entitled to compare themselves to distribution staff for equal pay purposes.

Store workers bringing claims are members of the GMB union, which hailed the ruling as “a massive victory”.

GMB legal director Susan Harris said: “We are proud to have supported our members in this litigation and helped them in their fight for pay justice.

“Asda has wasted money on lawyers’ bills chasing a lost cause, losing appeal after appeal, while tens of thousands of retail workers remain out of pocket.

“We now call on Asda to sit down with us to reach agreement on the back pay owed to our members – which could run to hundreds of millions of pounds.”

An Asda spokesperson said: “This ruling relates to one stage of a complex case that is likely to take several years to reach a conclusion.

“We are defending these claims because the pay in our stores and distribution centres is the same for colleagues doing the same jobs regardless of their gender. Retail and distribution are very different sectors with their own distinct skill sets and pay rates.

“Asda has always paid colleagues the market rate in these sectors and we remain confident in our case.”

Lawyers have said that if Asda store workers win all further stages of their fight they could be entitled to several years’ back pay.

They say this will have implications across the retail industry and suggested victory might lead to supermarkets paying out around £8bn.