Does this help
3.5.1 Employment by a spouse
Employment in the service of the husband or wife of the employed person is not insurable. However, where one member of a married couple is employed under a contract of service by a partnership consisting of the spouse and another person or persons, s/he will ordinarily be regarded as employed by the partnership and not by the spouse. This will also apply in the case of a limited company in which either member of the couple is a director. In each of these cases the spouse is not employed directly by the other spouse but through the partnership or limited company. The employment will be insurable if it is under a contract of service.