Could you try to deal with the problem a little subtly?
Why not provide the boy with a small soap bag with face cloth, soap, toothbrush and paste etc, and take him off and talk to him about the need to keep clean and healthy, maybe he could wash in core reading time. Maybe he has never been given the opportunity or educated to keep himself clean, we have had children with only cold running water in the house, with no heating - I know its not winter now, but who wants to wash in cold water in a freezing cold bathroom?
Maybe, as has also happened at my school, mum makes all the right noises, but does'nt provide him with toothpaste etc, and locks it in a cupboard for her and dad to use.
Maybe its a form of controlling abuse on her part.
Maybe, as has also been suspected before, this child does not want to be clean and presentable due to abuse that takes place when the child is clean and presentable, it may serve a purpose to be that disgusting that nobody will go near you.

No.....sadly we do have problems with children with lice.....we send a letter home to all parents if we spot lice/eggs but other than that we can do very little. I know the head has had a parent in for a discreet chat but she denied there was a problem, even saying she took her child to the health visitor who agreed there wasn't a problem....even though we could see them crawling.....I have to treat my kids weekly cos some parents don't bother....and yep, makes me seethe with anger at times