s 350 Connected person: child, spouse and civil partner
(1) In sections 118(2)(c), 188(1)(a), 200(1)(a) , 249(2)(a) and 280B(3)(a) , “ child ” includes a stepchild .... (2) For the purposes of sections 118(2)(e), 188(1)(b), 200(1)(b) , 249(2)(b) and 280B(3)(b) , where two people are not married to, or civil partners of, each other but live together as if they were a married couple or civil partners, each of them is to be treated as the spouse or civil partner of the other.