The concept of highest and best use is implicit in the theoretical basis of assessment of market value at a given point in time. Such value is understood to be ascertainable in accordance with the formulation of Isaacs J in Spencer's case:[32]
To arrive at the value of the land at that date, we have, as I conceive, to suppose it sold then, not by means of a forced sale, but by voluntary bargaining between the plaintiff and a purchaser, willing to trade, but neither of them so anxious to do so that he would overlook any ordinary business consideration. We must further suppose both to be perfectly acquainted with the land, and cognizant of all circumstances which might affect its value, either advantageously or prejudicially, including its situation, character, quality, proximity to conveniences or inconveniences, its surrounding features, the then present demand for land, and the likelihood, as then appearing to persons best capable of forming an opinion, of a rise or fall for what reason soever in the amount which one would otherwise be willing to fix as the value of the property.
It is implicit in this formulation that both vendor and purchaser are to be regarded as aware of the potentially most advantageous ongoing use of the land and not simply its current use, when formulating the relevant value. Such potential is a circumstance which necessarily affects the value of the land either advantageously or prejudicially.
Further, in Turner v Minister of Public Instruction[33] Dixon CJ stated:
After all the purpose (of valuation) is to ascertain the full return which may reasonably be expected from the sale of the land, not the most conservative value.
In Commonwealth Custodial Services Ltd v Valuer-General (NSW)[34] Biscoe J elaborated the concept by reference to relevant authority in the following terms:
There is no statutory definition of "highest and best use". It has been described in the High Court as "the most advantageous purpose for which [the land] was adapted": Spencer v The Commonwealth. It "is the present value alone of such advantages that falls to be determined": Cedar Rapids Manufacturing and Power Co v Lacoste. In Park v Allied Mortgage Corporation Ltd Hill J said at [70]: "As Spencer's case itself makes clear the valuation must proceed by reference to the best use of the property. For this purpose the valuer will take into account not only the present use to which the land is applied, but any more beneficial use to which it may reasonably be applied. This is the process which a purchaser negotiating to purchase the property would undertake. Thus, it is not inappropriate in valuing property to take into account a potential development of the property, for among the range of hypothetical purchasers can be assumed to be a person who would undertake such a development as would maximise the usage of the land". In Adelaide Clinic Holdings Pty Ltd v Minister for Water Resources Jacobs J said:
Common experience shows that land ideally suited for commercial development will fetch a higher price per unit of area than residential land, but it does not follow that the highest and best use of all land is a commercial use, for the highest and best use means exactly what it says - the most advantageous use of the subject land having regard to planning and all other relevant factors affecting its present and future potential. The first task of the valuer is to determine what that use is and then to value the land on that basis. It is not appropriate to determine the highest and best use by reference only to value.
In the present case the Tribunal summarised the underlying concept as follows in terms with which, with respect, we agree:
Highest and best use represents the most profitable potential use to which land can be put having regard to both planning and like controls and the circumstances of the land. It is to be distinguished from the present use of land; although the present use might also be the highest and best use. When land is sold, the market values the land at its highest and best use: as buyers will not be constrained to continue the existing use; and the seller will seek to achieve the highest price for the land. This is why highest and best use is relevant in assessing value, whether improved value or site value.
It also expressly referred to the notion of most advantageous use articulated by Jacobs J in the passage quoted above from the Adelaide Clinic case. Such a notion takes account of all factors relevant to the land affecting its present and future potential.
Further, as the Tribunal recognised in the course of its judgment, the highest and best use of a particular piece of land is flexible and may, at a particular point in time, be to "bank" the land with a view to future development rather than to use it actively.
By reference to s 5A, [of the VL Act] it can be seen that the Tribunal was required to take into account the highest and best use to which the land might reasonably be expected to be put at the relevant time and to any potential use where it was relevant. In the present case the question of highest and best use was potentially relevant both to the question of valuation generally pursuant to s 5A(1) and more specifically to questions of comparability of sales of other land pursuant to s 5A(2).
The language of the subsections is in our view deliberately flexible and capable of application to a potentially wide variety of circumstances as they may develop over time.
The role and weight to be given to the factor of highest and best use in a valuation exercise must in turn logically depend upon its relationship to other relevant factors disclosed by the evidence and affecting value.
This said, it was common ground between the parties that the proper ascertainment of the highest and best use of the subject land in the present case was a necessary preliminary step to its valuation. As Jacobs J stated in the Adelaide Clinic case in the passage already cited:
The first task of the valuer is to determine what that [highest and best] use is and then to value the land on that basis. [References in part omitted]