Head of the household?
A few years back, when the annual registration form arrived, I read the bit about the "head of the household" being prosecuted for not filling it in, and I wondered.
So I rang the ELO, and said, there are two adults living here - if you don't get the form filled in, who will you prosecute?
Er..... the owner of the house.
Nope - in joint names.
Er..... the one with the largest income?
Nope - no income, living on savings at the moment. And they're in joint accounts.
Er... I'll get back to you.
He never did, of course, because it is not a definable term in the modern world, so can only be applied in a single person household.