In calculating the maximum amount which may be demanded by the authority under section 35, such amount (if any) of the price or premium paid for the first relevant disposal which is attributable to improvements made to the house—
by the person by whom the disposal is, or is to be, made, and
after the conveyance, grant or assignment and before the disposal,
shall be disregarded.
The amount to be disregarded under this section shall be such amount as may be agreed between the parties or determined by the district valuer.
The district valuer shall not be required by virtue of this section to make a determination for the purposes of this section unless—
it is reasonably practicable for him to do so; and
his reasonable costs in making the determination are paid by the person by whom the disposal is, or is to be, made.
If the district valuer does not make a determination for the purposes of this section (and in default of an agreement), no amount is required to be disregarded under this section.