trust, and the property would be untraceable. Loss of the right to trace and defences The right to trace may be lost if the property cannot be found, or no longer exists. Defences to tracing are possible. The "change of position" defence is where the defendant has received property and giving it back would change his personal circumstances. This was concisely defined by Lord Goff in Lipkin Gorman v Karpnale as "Where an innocent defendant's position is so changed that he will suffer an injustice if called upon to repay or to repay in full, the injustice of requiring him so to repay outweighs the injustice of denying the plaintiff restitution". Such a defence is closely linked with unjust enrichment, and has limitations. Any bad faith on the part of the defendant will invalidate the defence, such as if the recipient of the property has encouraged the payer to transfer it or has received it by mistake and then used it without making enquiries. The defence is also not available to people who act illegally, as in Barros Mattos v MacDaniels Ltd. Activity which constitutes a "change of position" can be broadly defined as taking steps which would not otherwise have been taken, or not taking steps which otherwise would have been taken, as a result of receiving the property. Another defence is that of "estoppel by representation". This is similar to "change of position", and comes about when the defendant can show that the claimant made some false representation to him, which he acted upon to his detriment. Traditionally, the entire property would be the defendant's if the defence was successful. In National Westminster Bank plc v Somer International, however, the Court of Appeal decided that the defendant was only allowed to retain property equal to his losses due to the claimant's representation. Another defence similar to "change of position" is that of passing on, where the defendant has passed the property on to a third person without any benefit for the defendant; it is thus impossible to trace the property as the defendant has neither the property nor any proceeds from transferring it. Barriers to tracing Tracing can be barred in three types of situations. One is where property is in the hands of a bona fide purchaser for value without notice. This is when someone buys trust property with good faith not knowing that it is trust