The success of Part 36 depends on the clarity and certainty of its governing rules, see Gibbon v Manchester City Council. Accordingly, CPR 36.1(1) confirms that Part 36 is a self-contained code and, as a result, how Part 36 offers can be made, withdrawn, varied and accepted are all governed by CPR 36 and not the law governing the formation of contracts (see Practice Note: Part 36 offers—what are they, why make them?—Part 36 is a self-contained code). However, in O’Grady v B15 Group Ltd, it was held that the doctrine of common law mistake can apply to Part 36 offers in the specific circumstances of where there has been an obvious mistake in the making of the Part 36 offer. For the doctrine of common law mistake to apply in such cases, the offeror must show there was a clear and obvious mistake, which the offeree appreciated at the time when they accepted the offer. If the offeror is able to show this, there