Age UK’s website describes Age UK Energy as a "tailor-made gas and electricity package developed and provided by E.ON Energy Solutions Ltd".
Gary FitzGerald, chief executive of Action on Elder Abuse, has emailed organisations urging them to be cautious of the deal after The Times newspaper reported that it cost at least £200 more a year than the best existing energy deal for older people.
FitzGerald’s email said that Age UK’s offer "may not be all that it seems" and advises recipients to "cascade this email".
"Older people have enough to worry about at the moment, as the value of pensions is affected by soaring costs," it says. "Our advice is to tell people to read the small print, get independent advice and make sure that this is the deal they want."
Manna Santokhee, business and fund manager at Action on Elder Abuse, declined to discuss the matter further. He said FitzGerald was on holiday.
Gordon Morris, managing director of Age UK Enterprises, said the Action on Elder Abuse email was based on "a misleading comparison" and that "our energy tariffs are consistently cheaper and we benchmark prices with industry to ensure we are competitive".
Morris said the charity also provided an advice service that helped customers find the cheapest energy tariffs for their needs, even if it was not an Age UK product.
An Age UK spokeswoman said it had contacted Action on Elder Abuse to discuss the matter but had not heard back.
"We have sent a letter to The Times stating our position but it has not been printed," she said. "We are arranging for a follow-up meeting with the journalist."