QBD (TCC), 9 November 2006. Considered the application and meaning of the phrase unreasonably or vexatiously in the context of the issue of an initial notice of default and a notice of determination under a standard JCT contract. Claimant development company (R) was the employer under a contract with defendant contractor (B) to construct residential apartments. When the project overran and the contractual completion date passed a dispute arose regarding the payment of the balance of damages (an extension of time granted to B had reduced the amount of damages owed to R). B served a formal notice of default after R failed to effect payment by the final due date under the interim certificate. B then issued a notice of determination of the contract and left the development site when R failed to make a stage payment following a second interim certificate. R brought proceedings for declaratory relief on the basis that the notices were invalid and that B was not entitled to determine the contract. B sought by counterclaim that it had properly determined the contract. "Held": claim by R dismissed, judgment for B. B had not acted unreasonably in leaving the site and was entitled to determine the contract. "John Jarvis Ltd v Rockdale Housing Association Ltd" ([1986] 36 BLR 48) applied.