"additional support only for physically disabled"

This is what my 5 year old's school head is telling us at the moment. 

They are trying strategies to help him (calm box, comes in once kids are settled in class, home communication sheets etc.)

His teachers are struggling to deal with his uncontrolled emotions/ aggression/ stress/ constant questions.  They could really do with some one on one support for him.  Currently they have a classroom assistant some mornings who spends 99% of her time with him but won't be there next year.

Apparently the school can only receive funding for one on one support for a child if they have a physical disability.  

I am quite a chilled out and trusting mum but others have told me this may be a load of rubbish.

Who decides if my son can have additional support hours - the school, the council, the government?!  Any advice would be much appreciated!