7. The person liable to pay charges payable by virtue of these Regulations shall be the overseas visitor in respect of whom the services are provided except that—
(a)if the overseas visitor is employed to work on and for the purposes of a ship or vessel and is present in the United Kingdom in the course of such employment, the person liable to pay such charges shall be the owner of the ship or vessel on which the overseas visitor is employed; and
(b)if the overseas visitor is employed to work on and for the purposes of an aircraft and is present in the United Kingdom in the course of such employment, the person liable to pay such charges shall be his employer.