Expert determination, no-oral-modification clauses, and the limits on informal variations (GSY v Gladstone)
Construction analysis: The Technology and Construction Court (TCC) held that an expert determination was not binding where it rested on a contractual variation that could not legally occur. The parties’ agreements contained strict no-oral-modification (NOM) clauses, however the expert had treated informal conduct, including a lack of challenge to interim payment certificates, as creating a binding variation. The court applied MWB v Rock Advertising [2018] UKSC 24 and confirmed that NOM clauses must be enforced and that informal variations are ineffective unless the requirements for estoppel are clearly met. The court also applied the principles in Premier Telecommunications v Webb [2014] EWCA Civ 994, under which an expert’s determination will not bind the parties if the expert makes a material legal error or steps outside their contractual remit. On that basis, the expert’s determination that there had been a variation could not stand. The court granted summary judgment, leaving the underlying substantive issues to be resolved separately.