“Following the UKSC’s decision in Rock Advertising Ltd v MWB Business Exchange Centres Ltd  UKSC 24;  AC 119 that ‘no oral modification’ (NOM) clauses should be given effect unless the doctrine of estoppel arises, there was some uncertainty as to whether other common law courts would follow in that court’s footsteps. Much ink has also been spilled over the decision as well (for a summary, see Morgan, Great Debates in Contract Law, 3rd edn (2020), at p 86). A five-judge coram was specially convened in the Singapore Court of Appeal (SGCA) to hear this issue. Although in Charles Lim Teng Siang v Hong Choon Hau  SGCA 43 the SGCA found that the NOM clause in question was not engaged and it was not necessary to discuss the legal effect of NOM clauses, it indicated a strong preference for the position that, if the parties did subsequently agree to depart from the NOM clause, the courts will give effect to their oral agreement …”
Allen Sng Kiat Peng, ‘No oral modification clauses: the story from Singapore’ (2021) 137 Law Quarterly Review (Oct) 568.