Equitable Proprietary Estoppel This doctrine has sometimes been used to give effect to imperfect gifts – see, e.g. Gillett v Holt [2000] 2 All ER 289 and Thorner v Major [2009] UKHL 18. Proprietary estoppel arises where there is an assurance, reliance and detriment, so that it would be unconscionable to go back on the assurance. The award is based on the 'minimum equity required to do justice', so the claimant does not necessarily receive what he had been led to expect.