The Supreme Court unanimously held in a 26-page judgment that the claimants, who work in the retail business, can use the terms of conditions of employment enjoyed by employees in the distribution side of the business as a valid comparison.

The case hinged in part on the North hypothetical, which Lady Arden said is “important because otherwise an employer could avoid equal pay claims by allocating certain groups of employees to separate sites so that they can have different terms even where this is discriminatory”.

Barristers Andrew Short QC, Naomi Cunningham and Paul Livingston, from Outer Temple Chambers were instructed by Leigh Day in the case.

Lawyers for the 44,000 Asda workers, who are supported by the trade union GMB, will next argue that the roles are of equal value. If they are successful in this, Asda will then have an opportunity to argue that there is a reason, other than sex discrimination, as to why the roles should not be paid equally.

Leigh Day also represents clients from Sainsbury’s, Tesco, Morrisons, the Co-op and Next in similar equal pay cases which may be impacted by this judgment.

Employment partner Lauren Lougheed said: “We are delighted that our clients have cleared such a big hurdle in their fight for equal pay.

“Already an employment tribunal, the Employment Appeal Tribunal and the Court of Appeal ruled that these roles can be compared, and now the Supreme Court has come to the same conclusion.

“It’s our hope that Asda will now stop dragging its heels and pay their staff what they are worth.”

Susan Harris, GMB legal director, said: “This is amazing news and a massive victory for Asda’s predominantly women shop floor workforce. 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.”