A revised decision given by a deciding officer shall take effect as follows:

(a) where any benefit, assistance, child benefit, working family payment, continued payment for qualified children or back to work family dividend will, by virtue of the revised decision be disallowed or reduced and the revised decision is given owing to the original decision or determination having been given, or having continued in effect, by reason of any statement or representation (whether written or verbal) which was to the knowledge of the person making it false or misleading in a material respect or by reason of the wilful concealment of any material fact, it shall take effect from the date on which the original decision or determination took effect, but the original decision or determination may, in the discretion of the deciding officer, continue to apply to any period covered by the original decision or determination to which the false or misleading statement or representation or the wilful concealment of any material fact does not relate;