it is extremely routine for big companies to do this - all the fangs, big banks, etc, hire everyone they can in Britain on very pleasant pay packages and then hire overseas and pay immigrants the same amount.

Of course. And it's also a (deliberate, widely accepted) misunderstanding of basic economics. If you pay more you'll be able to hire more. Immigrants such as the one I'm replying to aren't typically hired because there are literally zero available locals with the skills. They're hired because they're cheaper, putting a ceiling on wages. Sometimes that ceiling can be quite high, but it's still there. "You can only bring someone into the country if you can't hire locally" is a polite fiction.