An inspector's powers to enter premises are not exercisable in relation to a part of premises that is used only for residential purposes except—
(a) with the consent of the occupier of the premises; or
(b) under a search warrant; or
(c) for gaining access to a suspected workplace, but only—
(i) if the inspector reasonably believes that no reasonable alternative access is available; and
(ii) at a reasonable time taking into account the times at which the inspector believes work is being carried out at the place to which access is sought.