From the ASDA link:
"Leigh Day, which represents 7,000 mainly female workers from Asda’s stores, says they are now able to lodge claims that they are paid less than other employees for doing “women’s work”.
The female workers in Asda’s shops say they are paid less than the mostly male workers in its distribution warehouses, despite their jobs being of “equal value”."
It appears the issue hinges on how one determines value. Is it a function of how heavy a box an employee can lift? How many transactions an employee can complete in an hour? How many items pass through an employees hands on their way to the sales floor or to a paying customer? How much value an employee adds through their skills as a meat cutter or fishmonger or pharmacist tech or childcare provider at the in-store supervised play area? It's not an easy call.
Salary isn't based on value. It's really based on demand. For example, often times a science or math teacher will be paid more than a music teacher because there are fewer math teachers than music. In the discussed case, it's generally more difficult to get people to work in a warehouse than in an air conditioned retail store.
You're assuming the working conditions in one are substantially better than the other. But even if that's the case and stores have to offer higher pay to staff their warehouses, the higher pay will attract job seekers of all genders. And anyway, we're talking about a largely unskilled workforce working for an hourly wage, not salaried employees.
There's no reason a woman can't pick goods off a warehouse shelf or a man can't place those same goods on a shelf in a grocery store.