21.—(1) Where a child support officer is not conducting a review under Article 18, 19 or 20 but is nevertheless satisfied that a maintenance assessment which is in force is defective by reason of—
(a)having been made in ignorance of a material fact;
(b)having been based on a mistake as to a material fact; or
(c)being wrong in law,
he may make a fresh maintenance assessment on the assumption that the person in whose favour the original assessment was made has made a fresh application for a maintenance assessment.
(2) Where a child support officer is not conducting such a review but is nevertheless satisfied that if an application were to be made under Article 19 or 20 it would be appropriate to make a fresh maintenance assessment, he may do so.
(3) Before making a fresh maintenance assessment under this Article, a child support officer shall give to such persons as may be prescribed, such notice of his proposal to make a fresh assessment as may be prescribed.