METHODS OF DEFEATING SUBJECTIVE DEVALUATION
If the defendant pleads the defence of subjective devaluation, it is open to the claimant to defeat this defence, either by proving that the defendant had received an incontrovertible benefit or by establishing that the defendant had requested or freely accepted the benefit.
(A) INCONTROVERTIBLE BENEFIT
The principle of incontrovertible benefit has been explicitly recognized in English law as a means to defeat the subjective devaluation principle.  The essence of incontrovertible benefit was identified by McLachlin J in Regional Municipality of Peel v Her Majesty the Queen in Right of Canada,107 a decision of the Supreme Court of Canada, where she described it as:
an unquestionable benefit, a benefit which is demonstrably apparent and not subject to debate and conjecture. Where the benefit is not clear and manifest it would be wrong to make the defendant pay, since he or she might well have preferred to decline the benefit if given the choice.
Consequently, incontrovertible benefit defeats the defendant’s reliance on subjective devaluation because it identifies those circumstances where it can be irrebutably presumed that the defendant would not have declined the benefit even if he or she had been given the choice to do so. In other words, the defendant will be incontrovertibly benefited where the only possible conclusion is that the defendant had received a valuable benefit. Treating the defendant as enriched in these circumstances will not infringe the defendant’s autonomy by making the defendant pay for a benefit he or she did not want since, by definition, the defendant must acknowledge that an incontrovertible benefit is a valuable enrichment to him or her. Obviously proof of incontrovertible benefit is not sufficient in its own right to establish unjust enrichment, since the other elements of the claim must also be identi- fied;1 8 the incontrovertible benefit principle is simply relevant to the identification of an enrichment.
Whether the defendant can be considered to have been incontrovertibly benefited will require careful analysis of the facts. For example, in J S Bloor Ltd v Pavillion Developments Ltd  it was held that the building of a road by the claimant, in circumstances where the defendant was contractually required to build it, was not incontrovertibly beneficial because, even though the defendant was benefited, it also suffered a detriment arising from the fact that it had not been able to design the road to its own specifications and had not negotiated the cost. In Benedetti v Sawiris Arden LJ had recognized that a defendant could not be incontrovertibly benefited by the receipt of services if the defendant never expected to pay for them. But this confuses the distinct questions of whether the defendant had been enriched and whether this enrichment is unjust. If the defendant did not expect to pay for the service, this would not prevent that service from being incontrovertibly beneficial, but it might indicate that there was no ground of restitution, since the basis for the performance of the service might be that it was to be paid for by somebody other than the defendant.
Although the determination of whether a benefit can be characterized as incontrovertible is ultimately a question of fact, five tests can be identified which will assist in the characterization of the benefit.
-  Benedetti v Sawiris  UKSC 50,  AC 938,  (Lord Clarke).
-  See especially Rowe v Vale of White Horse DC  EWHC 388 (Admin),  1 Lloyd’s Rep 418;McDonald v Coys of Kensington  EWCA Civ 43,  1 WLR 2775, 2789 (Mance LJ).
-  (1993) 98 DLR (4th) 140, 159.
-  It appears that this was ignored in Marston Construction Ltd v Kigass Ltd (1989) 15 Con LR 116.
-   EWHC 724 (TCC).
-   EWCA Civ 1427. This was not considered by the Supreme Court on appeal.
-  See further p 142, below.