Individual companies having a gender pay gap doesn't mean the market has a gender pay gap. And if you work at one of those companies and are told that you can't be given a raise because of the internal, secret gender pay gap, you should quit that company and find a new job.

I mean, even if it's true that particular company is paying its women worse than its men, and even if legislation means they can't quickly fix it (I don't know how onerous this legislation is in the U.K.), the proper response on the part of any employee who is given these excuses ought to be "Look, that sounds like you have a difficult problem, but that isn't my problem. My problem is that my salary is $X when it should be $X+Y." Because at the end of the day their excuses aren't going to change the fact that they can either fix your problem or not, and if they don't fix your problem somebody else in the labor market can.