I'm in North Wales, I don't know any heads with masters (or headmasters-we don't tend to differentiate between the sexes, we're all headteachers) However, when thinking about the question, most have come up through the ranks by being well-known to the LA. I mean by being outstanding class teachers who share practice throughout the authority. Foe example, if science is your thing, develop relationships with advisors, science advisors in other schools etc. Then they became deputies and again developed good networks so when they applied for headships the LA advisor on the governing panel knew the candidates well. But thats just my authority, in Wales. Good luck-it's the best job in the world most of the time.