The donor appointed A and B to act jointly, and then provided that "In the event A is unable or unwilling to act as my attorney then I appoint C." On the attorneys' application the court severed the appointment of C. Although a donor may appoint a substitute attorney, the appointment must not be incompatible with a joint appointment of the original attorneys. [OPG summary - EPA cases.]
The summary above is from the OPG website. Title: Re Bax (an order of District Judge S E Rogers made on 22 October 2009). Under the heading: "Appointment by donor of substitute attorneys".
Not on Bailii - no written judgment.
Summary on OPG section of Justice website