A retired senior judge has said power of attorney orders can have a "devastating" effect on families and said he would never sign one himself.
Denzil Lush, who was senior judge at the specialist Court of Protection for 20 years, which makes decisions over power of attorney, said the public needed to be aware the process could be open to abuse.
Power of attorney is a legal arrangement where people can hand decision-making over financial and welfare questions to a named person on their behalf.
Mr Lush, who has adjudicated 6,000 power of attorney cases, told BBC Radio 4's Today programme: "There tends to be a lack of transparency and accountability in attorneyship, which can have a devastating effect on family relationships, particularly between siblings and other family members."
He has previously estimated one in eight cases contained abuse.
Of the cases he has dealt with, he said around 90% of abusers were family members, while 68% were by a son or daughter.
He said: "I've seen the pathology over the last 20 years, I don't recall many cases where things have gone satisfactorily and to everybody's credit so I'm approaching it from that point of view.
"I would prefer a deputyship because there is accountability, there's supervision, there's security."
Deputyship, where someone is appointed to make decisions on your behalf, offers more scrutiny as assets and annual accounts need to be provided.
Some 650,000 applications were made for power of attorney last year, while there are two million already registered.
A Ministry of Justice spokesperson said: "Safeguarding vulnerable people is our priority.
"We take swift action if any abuse is reported and have a zero tolerance approach to any attorney or deputy who breaks the law.
"If there is evidence that someone has abused their position, we can refer cases to the Court of Protection to urgently revoke a lasting power of attorney or deputyship order."