The school cannot abdicate responsibility.
'The Children Act 1989 provides that teachers have a duty of care towards the children under their supervision, as well as promoting the safety and welfare of the children in their care and the Health and Safety at Work act 1974 puts a further obligation on the school as a whole to safeguard the wellbeing and safety of pupils in its care'
I'm sure the professionals amongst us could expand further on this but I'm sure that if some actions have been pointed out to the head teacher then some reasonable measures should have been taken to address the issues.