I've put the cat among the pigeons (as I expected I might...)
However, the notion that an English student who scored all A*s/9s in GCSE and A-levels (across the board) can't tutor current students on the best way to pass the exams with top grades is, frankly, ludicrous. Ironically (and I appreciate controversially) we have found good student tutors to be better than teachers across the board. I'm sure teachers are excellent with their classes, but on a 1-1 level it's not just about that, it's about rapport, more targeted improvement and, fundamentally, having a tutor that can use teacher/school feedback.
I strongly recommend using 'near peer' student tutors with a proven track record. They're cheaper, offer something different to standard schooling, and can be better than teachers.
I also note one theme about teachers knowing the syllabus and the 'change in emphasis of examiners'. To the extent that the 'emphasis' is more than a de minimis factor in reality, a good tutor will always review the syllabus and exam board updates. It's not gate kept information and it's entirely standard stuff. Fundamentally, at GCSE level, a 9 grade could be easily achieved by any competent and educated adult: the key is just in the effectiveness of the teaching/tutoring for each particular student. That might be good rapport, engaging tutoring techniques, recording lessons for revision purposes... and on it goes.
In any case, best of luck to everyone using a tutor! Each child clearly needs something different :)