What is the definition of work of equal value?

Asda has a set back in one particular employment law case:

They say they should be paid the same as those working in the supermarket's depots, who are mostly men.

The supermarket chain was challenging an Employment Appeal Tribunal decision that the jobs in Asda stores are comparable to those in its depots.

At the Court of Appeal in London, Lord Justice Underhill ruled that "Asda applied common terms and conditions wherever they [both types of workers] work".

That is, it is feasible to compare the jobs because they’re at the same employer under largely the same terms etc.

It’s this next bit:

The workers must still prove their roles are of equal value and, if they are, that there is no reason aside from sex discrimination that they should be paid equally.

To argue about the value of work is to commit a category error. It’s, effectively, to be making Marx’s mistake with the labour theory of value. Since the 1870s and the marginalist revolution we’ve known that’s wrong. We need to consider the supply of workers able to do the job and the demand for them to do so - that’s what determines those wages.

Only after that error do we get to the next, which is any decision to insist that two different jobs are of equal such value. The only measure we’ve got - only useful one - of what a job’s worth is what someone is willing to pay to get it done. How can it be otherwise in a market economy?

The entire concept being used here is thus wrong. A sad thing to have to say about what we’ve, in error, encapsulated into law.