From Mental Health Law Online
The donor had been appointed to act as attorney under LPAs made by his wife. In his own LPA for property and financial affairs he stated as follows: "In the event that I become incapacitated and am unable to take decisions in my role as Attorney to my wife, I appoint both my Attorneys as Guardians of my wife in order that they may, together, take decisions about her property and affairs." He included an equivalent provision in his LPA for health and welfare. On the application of the Public Guardian the court severed these provisions as being ineffective because the MCA does not permit an attorney to appoint a substitute or successor to himself. (OPG summary - LPA case.)
The summary above was taken from the OPG website. Title: Re Swift (an order of the Senior Judge made on 30 March 2010). Heading: Appointment of substitute by an attorney.
No Bailii link - no written judgment