Can extrinsic evidence be adduced to prove that a consideration was not stated in a written deed?

In the present case, the evidence does fall within one of the established exceptions to the rule: extrinsic evidence may be adduced for the purpose of showing that the true consideration was something more than the consideration stated in a written instrument. This exception to the rule has its roots in Clifford v. Turrell (1841), 62 E.R. 826, aff'd 14 L.J. Ch. 390 wherein it was held, at 830: The rule is that, where there is one consideration stated in the deed, you may prove any other consideration which existed, not in contradiction to the instrument; and it is not in contradiction to the instrument to prove a larger consideration than that which is stated [emphasis added].