In "the" field?
I'm not sure what field you're referring to with the following:
"What is the point in kids A-Level physics when physics graduates can't get work in the field (my brother who has an MPhys being a case in point)."
Physics doesn't fit into just one neat little field, it's used from everything from engineering to space exploration to games programming so it's hard to know what this mystical field you're talking about is.
As a mathematician and a computer scientist I see this a lot, many people go through school, a-levels, degrees and get their qualification in maths then ask what to do with it, being unable to find anything listed in the job paper saying "Mathematician" then then cry that maths is useless and was pointless studying. This is absolutely the wrong way to go about maths and physics, it's not like say, IT where you go get your IT degree and work in IT any old place, because IT is the same, you instead have to look first at the industry you wish to work in and then realise for yourself how math is applied there and then you can find the jobs.
Want to work in the fashion industry? They need mathematicians to carry out statistical studies as to how big a size medium should be to be able to fit the average person. Want to work in the finance sector? Plenty of math use there. How about the defence industry? Again, no shortage of requirements for people skilled in number theory to be used in encryption, or maths with mechanics to calculate how various subsystems in a product are going to work.
The fact is, not everything is handed for you on a plate when you follow the GCSE -> A-Level -> Degree drone-route, sometimes you actually have to figure out for yourself what you're doing with your life, with your qualifications and put some effort into pursuing it.
What irks me the most about it all is that some people are clever enough to complete a math/physics degree to a high level but too dumb to even know what they're actually going to do with it. What an absolutely horrible waste of what could otherwise be an intelligent person, perhaps alongside majors in physics we need to begin to add in some minor classes in motivation and common sense.