and/or does anyone know what the official policy is?
At our school a 'regular full timetable' is 22 out of 25 (1-hr lessons) plus a form group.
Current NQTs have 21 out of 25 lessons, but no form group. I think this is quite stingy, and is considerably more than NQTs in the recent past. In their 'free periods' they also have 1 hr per week with a subject mentor, and 1 hr per week with NQT supervisor.