Next could face an equal pay claim from its mainly female shopfloor staff, who are paid less than their warehouse colleagues.

More than 300 of its workers have registered to take part in the claim for backpay, filed at conciliation service Acas yesterday, according to The Guardian.

They allege that they are paid £7.50 per hour, around £2 less than their counterparts in Next warehouses, who are usually men. Warehouse employees also have access to better bonus schemes.

The average salary “loss” across the 300 people taking part is around £6,000. It is estimated that around 3,000 to 5,000 employees will ultimately sign up. If 5,000 workers do sign up, Next could be facing a £30m claim.

The retailer employs 45,000 people in the UK, two thirds of whom are women working on the shop floor.

The claim is the first of its kind outside the grocery sector. All of the big four supermarkets have faced or face potential claims, with Tesco staff currently demanding £4bn in backpay – the largest pay claim ever in Britain.

Elizabeth George, head of employment at law firm Pattinson Brewer, which is representing the Next claimants, told The Guardian: “Shopfloor work was always perceived as women’s work and so thought to be worth less than work in the warehouses, which was traditionally perceived as men’s work.

“It is open to Next to approach these claims differently from say, Asda. They can spend months (possibly years) fighting the claims or they can take a radically different and progressive approach and work with us to put this problem right.”

A spokesman for Next said he was unaware of any filing.

He added: “The difference between working in a warehouse and a store at Next is, however, more significant than for any of the retailers now involved in litigation.

“Next values all its employees, regardless of their gender, role and place of work within the business. Next is also confident that all its employees are paid legally, fairly and appropriately for the jobs they perform.”