In this day and age, I suspect that 95% of the people at Silverstone for any sort of event will never have seen a low flying military jet, due to living in the middle of a very large built up area such as Brum, London, Manchester, etc. The people most likely to have exposure to military heavy metal are rural dwellers, who probably wouldn't blink at the sight of a low flying jet - however there obviously aren't as many of them, particularly in that part of the world.
With regards to reactions on PPRuNe, you will generally get a serious reply, but only after 15 bone or tongue in cheek replies. Be patient!
