79.—(1) Except in cases to which paragraph (2) refers, where, on the revision of a decision allowing council tax benefit to a person, it is determined that the amount allowed was less than the amount to which that person was entitled, the relevant authority shall either—
(a)make good any shortfall in benefit which is due to that person, by reducing so far as possible the next and any subsequent payments he is liable to make in respect of the council tax of the authority concerned as it has effect for the relevant chargeable financial year until that shortfall is made good; or
(b)where this is not possible or the person concerned so requests, pay any shortfall in benefit due to that person within 14 days of the revision of the decision being made or if that is not reasonably practicable, as soon as possible afterwards.
(2) A shortfall in benefit need not be paid in any case to the extent that there is due from the person concerned to the relevant authority any recoverable excess benefit to which regulation 83(1) refers.