With respect to the concerns expressed in previous cases regarding partisan autonomy and conceptual inconsistencies between (i) a general rule authorizing informal contracting (z.B oral) and (ii) a specific rule that would take effect on contracts requiring written changes, the majority considered that there was no inconsistency: that the parties do not allow , in a nomadic clause, to rule later on a number of amendments to amend the treaty informally (autonomy), but that any informal agreement that does not meet the formal requirements they have set will be ineffective (although the practical effect is of course the same). Some types of contracts must be written (and any derogations must be written), for example. B contracts for the sale of land and disposals for a contract. As we saw in Rock, the contract may require that any changes be made in writing and signed. The agreement is simple: when amending the terms of an agreement, it is advisable to do so in writing in order to create a particular position – and a written amendment may be essential depending on the terms of the underlying contract. The parties should also carefully consider the impact of any changes to the proposed provisions on the existing provisions. Invocation of the behaviour of contractual value may be problematic because of evidenties. In the event of a dispute over whether the parties have entered into a valid agreement to renew the contract, the Tribunal will rule on the issue on the relevant facts, taking into account the usual rules of interpretation of the contract. TRW is therefore in a contractual relationship with a subsidiary of its parent company, which is much less financially stable. TRW had submitted that it had never accepted such a variant and that tSMmen had withdrawn the financial protection that TRW had had through a contract with a major organization such as Globe.
On the other hand, the Globe Porto Balance Sheet was weak, so that TRW would have had no recourse or had only limited recourse in the event of supply or quality problems. The recent case of Rock Advertising v MWB Business Exchange Centres Limited  confirmed that a contract that does not contain an oral non-amendment clause (NOM) cannot be amended orally. He also raised the question of how multiple contracts are and what differences there are, says Martin Collingwood There were two competing decisions of the Court of Appeal on this subject – therefore, it was legitimate to decide which one was to follow. They preferred the approach that recognizes the principle that a contract containing a non-variation clause can effectively be changed by oral agreement or conduct. In trade agreements, it is customary to include a provision that changes to a contract are null and void, unless they are written and signed by or on behalf of both parties. This is called the variation clause and is intended to avoid informal or involuntary oral variations. However, the common law allows for the amendment of a written contract by the mutual consent of both parties, either orally or in writing. This can complicate the position. On the other hand, derogations from the performance of this work are generally carried out according to a method of variation established in the contractual conditions.