Although the principle is not entirely clear, it seems that a concession, waiver, variation, or forbearance promised by one party to the other will be enforced in equity subject to proper notice being given to the other party of the resumption of the strict contractual provisions. Proper notice will involve the honouring of any time period contained in the original concession, otherwise, equity will insist on a reasonable period of notice: Charles Rickards Ltd v Oppenheim [1950] 1 All ER 420. There would appear to be a high degree of similarity between waiver and promissory estoppel, the general view being that they are related, yet distinct, doctrines that produce the same effects.