The UK Supreme Court decision in Szepietowski & Anor v National Crime Agency  UKSC 65 examined whether the remedy of marshalling was available to the National Crime Agency (NCA) in the absence of an underlying debt. The NCA entered into a settlement deed with Szepietowski that established rights over some of Szepietowski's properties, but did not create or acknowledge any debt on the part of Szepietowski. The NCA's claim was secured by a second mortgage over one of the Szepietowski's properties (Property). The first mortgagee, despite having adequate security over other properties, exercised its power to sell the Property. The NCA sought the equitable remedy of marshalling in order to allow it to enforce the first mortgagee's remaining mortgages instead.
Lord Neuberger held that when the mortgagor does not owe a debt to the second mortgagee, the remedy of marshalling is generally not available. This position is not subject to judicial discretion, and only exceptional circumstances may justify marshalling in the absence of a debt. This is because there is simply nothing due after the secured property is sold, and a second mortgagee is effectively in a lesser position than an unsecured creditor. Allowing marshalling would therefore be disadvantageous to the mortgagor and to unsecured creditors in a potential insolvency event.
See Court decision here.