Secured creditors of Lehman Brothers Holdings’ London-based subsidiary expected to be voting this fall on a hard-fought plan for getting around $16.7 billion of their assets back. Instead, the U.K. administrator overseeing the bankruptcy, PricewaterhouseCoopers, will be trying to salvage the plan from a damaging court ruling handed down in late August.

To expedite the return of client cash and collateral, the administrator had asked the court to bless the use of a legal process in the U.K.,...