On the subject of MPs and STEM backgrounds, I don't think we have moved on much from CP Snow's Two Cultures over 50 years ago:
"A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientific equivalent of: Have you read a work of Shakespeare’s?
I now believe that if I had asked an even simpler question — such as, What do you mean by mass, or acceleration, which is the scientific equivalent of saying, Can you read? — not more than one in ten of the highly educated would have felt that I was speaking the same language. So the great edifice of modern physics goes up, and the majority of the cleverest people in the western world have about as much insight into it as their neolithic ancestors would have had."
I just looked up David Cameron's A-Levels. He would seem to be a remarkably intelligent and well-educated individual - he did History of Art,
History and Economics with Politics. I guess without his background people would look at that selection and say 'so you don't want to be able to get a job then?'