This is more complicated than it seems and you will need to talk to the Elections Officer of your principal authority. It depends which boxes the individual ticked on their nomination papers for the most recent election, assuming he or she was elected, even if unopposed. There are four different means by which somebody may qualify, namely:
(a) I am registered as a local government elector for the area of the parish named above
(b) I have, during the whole of the preceding 12 months occupied as owner or tenant land or other premises in the parish named above
(c) my principal or only place of work during the preceding 12 months has been in the parish named above
(d) I have during the whole of the preceding 12 months resided in the parish named above or within 4.8 kilometres of it.
If the individual ticked only box (a), they cease to be a member of the council on the day they are no longer included on the electoral register. If they ticked any of the other boxes, either individually or in tandem with box (a), they remain a member of the council until the end of their term of office at the next scheduled election, unless they resign beforehand. The qualifying criteria may not be applied retrospectively and must be those written on the original form.