While the debate rages on the original post, allow me to throw in my tuppence worth.
It strikes me that junior doctors are not particularly underpaid, they are just crassly overworked (starting salary £30,000 for 100 hours a week, or whatever). The reverse applies to more senior doctors.
According to the BMA, senior doctors (under whatever fancy title) are paid up to £180,000, probably for working about 20 hours a week.
My policy would be to flatten the pay scale and flatten the working hours as well, so that junior doctors start on £40,000 for 60 hours a week and the senior ones are paid £120,000 for 30 hours a week, for example. Or they all get £80,000 for 45 hours, or whatever, in line with what GPs currently get.
So instead of this being BMA vs NHS/taxpayer, the NHS can just set a total budget for doctors' and GPs' pay and let them fight it out among themselves.