Money is only a symptom. What it's really about is the vestiges of the old British class system. Doctors, lawyers, bankers, managers, and so on are upper-middle-class professionals. Engineers of any sort, no matter how skilled, no matter how many degrees, PE or CEng status, have the taint of blue-collar about them (from the POV of the upper-middles). A manager will never be happy to see a worker paid more than him, even if by the laws of supply and demand they ought to be.

This is much much less of a problem in say Germany where Engineer is a respected, prestigious title in its own right.