It must be inequitable for the promisor to go back on the promise

Payment of part of a debt will not usually be sufficient consideration for a simple promise to forego the balance. This is known as the rule in Pinnel’s case. The rule was reaffirmed by House of Lords both in Foakes v Beer,38 and, more recently, in Re Selectmove Limited.39 It now appears to be generally accepted that promissory estoppel may be used to mitigate the harshness of the rule in Pinnel’s Case, provided that all the conditions discussed above are met.