In Waller-Edwards v One Savings Bank Plc,1 the Supreme Court allowed an appeal from the Court of Appeal,2 and partly restated the law on the O’Brien/Etridge formula. In brief, the decisions of the House of Lords in Barclays Bank Plc v O’Brien 3 and Royal Bank of Scotland Plc v Etridge (No 2)4 had established a regime under which lending banks would in certain circumstances be unable to enforce a secured guarantee of a loan where the surety had been subject to undue influence or other wrongdoing on the part of the borrower. In O’Brien the typical scenario in issue was a wife guaranteeing a loan to her husband’s business and executing a mortgage over the couple’s matrimonial home as security. Without providing any definition of the type of relationship that would engage the legal regime being laid down, the speech of Lord Browne-Wilkinson in O’Brien indicated that it extended to other emotional or family relationships as well. O’Brien was understood to hold that, if the transaction was not on its face to the surety’s advantage and there appeared to be a risk that the surety entered into the guarantee subject to the undue influence or other wrongful conduct of the borrower, then the lender would have to ensure that the surety was independently advised. If it failed to do so, then it would be unable to enforce the guarantee and its security against the surety. Etridge restated the law in terms that eliminated any need for the transaction to appear to be not to the surety’s advantage or exhibiting particular risks that the borrower’s wrongful conduct had procured it. Instead, the lender could obtain protection against the borrower’s wrongful conduct only by arranging independent legal advice in any case where the relationship between