I read it as part of a case [1] Judgment; used as follows:
1.)
If the creditor bank has notice, actual or constructive, of the undue influence exercised by the husband (and consequentially of the wife's equity to set aside the transaction) the creditor will take subject to that equity and the wife can set aside the transaction against the creditor (albeit a purchaser for value) as well as against the husband.
2.)
Where a wife has agreed to stand surety for her husband's debts as a result of undue influence or misrepresentation, the creditor will take subject to the wife's equity to set aside the transaction if the circumstances are such as to put the creditor on inquiry as to the circumstances in which she agreed to stand surety.
[1] Barclays Bank plc v O'Brien [1994] 1 AC 180, House of Lords
Thank you.