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[1981] AC 513 (HL). A father granted his son the right to purchase his farm. This OptionToPurchase was validly created, but the son did not register it (he should have used a class C(iv)land charge). Later the father and son fell out, and the father sold the farm to his wife for £500, a fraction of what it was worth. It was clear that she knew the about the earlier option in favour of the son, and that the sale was intended solely to thwarte the son's rights.

In the Court of Appeal, the son's action to enforce the option succeeded, as equity did appear to demand. Now, the land charges act (1972) makes registration of a land charge equivalent to notice of that charge. By necessary implication, if a charge that must be registered is not registered, the owner of the charge is prevented from enforcing it against certain categories of person who take a later interest in the estate. In the case of class C(iv), an interest in that class is unenforceable against a 'purchaser of the legal estate for value' if it is not registered. The wife did offer an amount which would have constituted good Consideration in contract law, and the son's action ought to have failed on that ground. However, the Court of Appeal interpreted 'purchaser for value' as meaning a person who offered an adequate sum for the land, and clearly the purchaser in this case had not done so.

In the House of lords, the decision was reversed; the House stressed that 'purchaser for value' had its ordinary, contract law meaning. It was not for the court to enquire into whether the consideration was adequate or not.