My understanding is if neither parent or the parent with the majority of
care isn't eligible for Child Benefit it would be deemed a special case.
Currently the presumption in the first instance is the person
in receipt of CB is the parent with care but in special cases the CSA can
determine who is
PWC. I think I posted a link to the relevant
regulations sometime towards the end of last week.
There is
something similar in the draft regulations (perhaps somewhere around number
50-60 if memory serves me well).