An undertaking given under section 78 or 79 above may be varied from time to time by agreement between the Board and the person bound by the undertaking.
Where the tribunal is satisfied that—
the Board have made a proposal for the variation of such an undertaking to the person bound by the undertaking,
that person has failed to agree to the proposed variation within six months after the date on which the proposal was made, and
it is just and reasonable, in all the circumstances, to require the proposed variation to be made,
the tribunal may direct that the undertaking is to have effect from a specified date as if the proposed variation had been agreed to by the person bound by the undertaking.
The date specified by the tribunal must not be less than sixty days after the date of the tribunal's direction.
A direction under this section shall not take effect if, before the date specified by the tribunal, a variation different from that to which the direction relates is agreed between the Board and the person bound by the undertaking.