No child benefit shall be payable in respect of a child F2or qualifying young person for a week unless he is in Great Britain in that week.
(2)
No person shall be entitled to child benefit for a week unless he is in Great Britain in that week.
(3)
Circumstances may be prescribed in which F3any person is to be treated for the purposes of F4subsection (1) or (2) above as being, or as not being, in Great Britain.