1.—(1) A claimant is to be treated as liable to make payments where the person who is liable to make the payments is—
(a)any child or qualifying young person for whom the claimant (or if the claimant is a member of a couple, either member) is responsible, or
(b)in the case of a claimant who is a member of a couple claiming as a single person, the other member of the couple.
(2) Sub-paragraph (1)(b) does not apply to a person who is claiming as a single person by virtue of regulation 3(3) (polygamous marriages).