According to the so-called 'parol evidence rule', extrinsic evidence, oral or otherwise, may not be adduced which seeks to add, vary or contradict the terms of a written contract. Thus, in Jacobs v Batavia & General Plantations Trust [1924] 1 Ch 287 it was stated that: 'parol evidence will not be admitted to prove that some particular term, which had been verbally agreed upon, had been omitted (by design or otherwise) from a written instrument constituting a valid and operative contract between the parties'.