I don't know much detail, but you certainly don't have any right to flexi-schooling - it is always an agreement between the head teacher and the parent, but it's entirely up to the school whether they let you do it or not.
I think there are complications about how the school are funded, and how they have to fill in the child's attendance sheet to make sure it doesn't impact on their stats.
You don't have any rights to it, you have to persuade the head. We tried and failed dismally. I also know of another lady flexischooling her child, but it transpires she got it on medical grounds because the child was quite ill last year. Now she is much better the school are saying, you come full time or not at all
For us, it worked well, because it pushed us into home education which was a great decision. But we were quite despondant at our lack of success at the time.
Hi. As well as not having the right to choose flexi-schooling, most schools aren't keen (although I do know of a school round my way that - reluctantly - agreed to do it).
Also, if a child is flexi-schooling, they then have to follow the National Curriculum (if they're in a state school) as this is obligatory for registered state school pupils.
I don't think there's a minimum time they have to spend in school, though.
We asked our local secondary school about flexi-schooling when DS2 (home educated) reached secondary school age but they said no - they were horrified at the very idea - so we've been happily home educating through the secondary school years as well.