Barclays Bank plc v O’Brien [1993] UKHL 6 (21 October 1993) is an English contract law case relating to undue influence.

Mr Tucker, who worked for Barclays Bank plc, when the mortgage was increased to £60,000 in 1981 made a note that Mrs O’Brien might be a problem.

Purchas, Butler-Sloss and Scott LJJ said it was "artificial" to find undue influence on the basis that a spouse (or other relative) was acting as the bank's agent in obtaining a signature for a charge.

In Bank of Credit and Commerce International SA v Aboody (1988) [1992] 4 All ER 955 at 964 the Court of Appeal helpfully adopted the following classification.

Class 2(A) Certain relationships (for example solicitor and client, medical advisor and patient) as a matter of law raise the presumption that undue influence has been exercised.

In a Class 2(B) case therefore, in the absence of evidence disproving undue influence, the complainant will succeed in setting aside the impugned transaction merely by proof that the complainant reposed trust and confidence in the wrongdoer without having to prove that the wrongdoer exerted actual undue influence or otherwise abused such trust and confidence in relation to the particular transaction impugned.

The idea of a private meeting was put forward by Lord Browne-Wilkinson in his judgment:for the future in my judgment a creditor will have satisfied these requirements if it insists that the wife attend a private meeting (in the absence of the husband) with a representative of the creditor at which she is told of the extent of her liability as surety, warned of the risk she is running and urged to take independent legal advice.

[4] The decision in O'Brien was handed down on the same day as CIBC Mortgages plc v Pitt [1993] UKHL 7 (21 October 1993) (where Lord Browne-Wilkinson also gave the only speech).