Mr Jennings, a self-employed bricklayer and part-time gardener, sued the administrator of his former employer, Mr. Arthur Thomas Rice, for a large house and furniture (worth £435,000) on the basis that he had been given an assurance he would get it.
After a burglary in 1993, Mr. Jennings was persuaded to sleep overnight and eventually his responsibilities extended to helping her dress and go to the toilet, collecting her prescriptions and making sure she had enough food and drink available.
The judge held that in the late 1980s, Mr Jennings had challenged Mrs Royle about her failure to pay him and she assured him that he need not worry.
It cannot be doubted that in this as in every other area of the law, the court must take a principled approach, and cannot exercise a completely unfettered discretion according to the individual judge's notion of what is fair in any particular case.
I do not think that the judgment of Hobhouse LJ in Sledmore v Dalby (1996) 72 P&CR 196 (to which I shall return) can possibly be regarded as adopting or advocating an unfettered judicial discretion.
But it is unlikely to be a short or simple search, because (as appears from both the English and the Australian authorities) proprietary estoppel can apply in a wide variety of factual situations, and any summary formula is likely to prove to be an over-simplification.
The doctrine applies only if these elements, in combination, make it unconscionable for the person giving the assurances (whom I will call the benefactor, although that may not always be an appropriate label) to go back on them.
In a case like that the consensual element of what has happened suggests that the claimant and the benefactor probably regarded the expected benefit and the accepted detriment as being (in a general, imprecise way) equivalent, or at any rate not obviously disproportionate.
In Re Basham [1986] 1 WLR 1489 the deputy judge (Mr Edward Nugee QC) rejected the submission that there must be some clearly identified piece of property, and that decision has been approved more than once in this court.
Moreover (as the judge's findings in this case vividly illustrate) the claimant's expectations may have been formed on the basis of vague and inconsistent assurances.
Scarman LJ's well-known reference to "the minimum equity to do justice to the plaintiff" (Crabb v Arun District Council [1976] Ch 179, 198) must no doubt be read in the context of the rather unusual facts of that case, but it does not stand alone.
As Scarman LJ recognised, the line of authority goes back to nineteenth-century cases such as Duke of Beaufort v Patrick (1853) 17 Beav.60 and Plimmer v Wellington Corporation (1884) 9 App Cas 699.
To recapitulate: there is a category of case in which the benefactor and the claimant have reached a mutual understanding which is in reasonably clear terms but does not amount to a contract.
But the detriment of an ever- increasing burden of care for an elderly person, and of having to be subservient to his or her moods and wishes, is very difficult to quantify in money terms.
Moreover the claimant may not be motivated solely by reliance on the benefactor's assurances, and may receive some countervailing benefits (such as free bed and board).
The judge did in this case consider, although not in detail, what Mr Jennings might reasonably have earned in the way of arm's length remuneration for his services.
A detailed computational approach was adopted (but with a different outcome, limited to compensation of reliance loss) by the Supreme Court of Tasmania in Public Trustee v Wadley [1997] 7 Tas.
LR 35 in which the court discussed the appropriate hourly rate and the total number of hours of housework undertaken by a daughter who (as it was put in the dissenting judgment of Wright J) "had subordinated her own life to that of her father and [whose] attentive and affectionate service, often no doubt at considerable inconvenience to herself, put her assistance on a higher plane than that of a domestic servant".
However I respectfully agree with the view expressed by Hobhouse LJ in Sledmore v Dalby (1996) 72 P&CR 196, that the principle of proportionality (between remedy and detriment), emphasised by Mason CJ in Verwayen, is relevant in England also.
As Hobhouse LJ observed at p.209, to recognise the need for proportionality "... is to say little more than that the end result must be a just one having regard to the assumption made by the party asserting the estoppel and the detriment which he has experienced."
Cases on interim injunctive relief have recognised the importance of proportionality in the granting of equitable remedies: see for instance Lock International v Beswick [1989] 1 WLR 1268, 1281.
He did make an error in his reference to the quantum of the relief granted in Gillett v Holt (the claimant was awarded a farmhouse and 42 hectares of land as well as £ 100,000).