I think this whole obsession that schools in england have with childrens' hair is bizarre full stop.
Why does an establishment that a child spends less than 20% of their week in get to dictate how that child looks for the other 80%?
I'm ambivalent about uniform but if there is a uniform that should be worn during the school part of the day fair enough. Health and safety applies to hair, should be tied back during appropriate lessons (PE/Science experiments/cooking etc.
How would you feel if school told you how DC have to look in the evenings or weekends or what PJs they should wear? You'd tell then to get stuffed wouldn't you? So why are parents allowing school to tell them how long or short a child's hair should be? Or what colour it is or whether they can grow a beard for that matter.