An offer is an expression of willingness to contract on certain terms. It must be made with the intention that it will become binding upon acceptance.An offer is a proposal from one party to another intending to create a legal obligation upon acceptance. Acceptance in contract law is when a person agrees to the terms of an offer without any changes. In this article, we will unravel the intricacies of offer and acceptance in the context of UK law, providing clarity and insight for undergraduate law students. Common Law: Traditional "Mirror Image" Rule. The traditional contract law rule is that an acceptance must be the mirror image of the offer.