An investigation will take place into whether charities are buying and selling personal information amid claims an elderly man was conned out of thousands of pounds.
Widower Samuel Rae's details were passed on hundreds of times after he forgot to tick a box on a lifestyle survey 21 years ago, the Daily Mail claimed.
The 87-year-old former army colonel's data has since been given to charities, and even some companies associated with scams with the result that he has lost almost £35,000, the newspaper alleged.
The Information Commissioner's Office (ICO) said the claims were "clearly concerning".
"We will be investigating whether any breaches of the law have taken place," Steve Eckersley from the ICO told the paper.
"The law applies to charities as it does to any other organisation.
"If charities are buying and selling personal information without any thought of the wishes of the people involved it suggests not only a disregard for the law, but also a disconnect with the supporters whose generosity they rely on.
"Unfortunately it isn't the first time we've been presented with evidence suggesting bad practice in the charity sector."
Mr Rae's son Chris said his father, who lives in St Buryan in Cornwall and suffers from dementia, had been treated in an "absolutely disgraceful" way by charities.
He told the paper: "If what they have done to my father is legal, then the law needs to change.
'I'm just appalled and deeply shocked."
He said the case illustrates what can happen if someone forgets to tick a box on a form asking for their details not to be shared.