I'm going to throw in my tuppence worth as a union leader here in Australia, albeit a much smaller constituency than the NUT.
Here, we have one national union with each state being a branch of the same union. We have 95% membership in some states and we are the strongest union in the country - BECAUSE WE ARE UNITED and do not have to waste time on fighting/disagreeing with competing unions. We achieve conditions for teachers which are the envy of other countries because our union is not split on issues and we represent all teachers, including Principals. I would suggest that is one of Britain's teacher unions' major problems. However, whether it could ever be achieved is another question.
My salary as President of the State Branch, as in the other six states, is about the same as that of a large-school principal or what we call a "district superintendant". It probably equates to 45,000 pounds, plus a car, in real cost-of-living terms.The salary is set at this level so that any member winning the position will not be disadvantaged. (I am the first unpromoted classroom teacher ever to be elected) As the position means that I am the officer responsible to the whole membership, the one who can be "sued", and that I have to liase with the Education Minister etc. I believe this level of salary is appropriate.
I agree with many of the comments here that teachers' conditions in Britain are appalling. I have taught there and am amazed with what they have to endure. I fervently hope that whoever the next NUT Secretary is, he (no women, I gather?) will fight for and win some better deals for teachers, because all I hear on various teacher chatlines I belong to, is the overwhelming desire among British teachers to get out before the profession kills them.