3.—(1) Any relevant decision may be revised or further revised by the relevant authority which made the decision—
(a)either within the prescribed period or in prescribed cases or circumstances; and
(b)either on an application made for the purpose by a person affected by the decision or on its own initiative,
and regulations may prescribe the procedure by which a decision of a relevant authority may be so revised.
(2) In making a decision under sub-paragraph (1), the relevant authority need not consider any issue that is not raised by the application or, as the case may be, did not cause it to act on its own initiative.
(3) Subject to sub-paragraphs (4) and (5) and paragraph 18, a revision under this paragraph shall take effect from the date on which the original decision took (or was to take) effect.
(4) Regulations may provide that, in prescribed cases or circumstances, a revision under this paragraph shall take effect from such other date as may be prescribed.
(5) Where a decision is revised under this paragraph, for the purposes of any rule as to the time allowed for bringing an appeal, the decision shall be regarded as made on the date on which it is so revised.
(6) Except in prescribed circumstances, an appeal against a decision of the relevant authority shall lapse if the decision is revised under this paragraph before the appeal is determined.