Charities that sold donor data earned as little as about 6p per name passed on, a BBC radio documentary has revealed.
The Radio 4 programme, called Selling Barbara and broadcast this morning, focused on 90-year-old donor Barbara Smith, who wanted to find out why charities had passed her details to other voluntary sector organisations, which had been contacting her asking for money.
In the programme, Smith spoke to Mark Roy, chair of the data company the REaD Group, and asked him how much charities received for selling names of donors.
"Usually data is sold on a cost-per-thousand basis," said Roy. "It would vary between about £60 and £300 a thousand.
"So if, for instance, you're a known giver to cancer charities, then absolutely you'd be up at the top end of £300 per thousand.
"The bad thing for you is that means your name is worth about 30p."
Where the data was sold for £60 per thousand, it would mean each name passed on would be worth 6p.
The Code of Fundraising Practice was changed in 2015 to prevent charities selling donors' data, though sharing is still permitted in certain circumstances.
Susu Stinton, chair of Smile Train UK, which shared Smith's data with 10 other charities, talked to Smith as part of the programme.
Stinton said it had been a couple of years since Smile Train had shared data with any other charity but said the practice had been commonplace in the voluntary sector.
"Imagine you're a small charity," she said. "How do you contact people?"
She said one way to get details of potential donors would be from another charity. "If you know somebody is already a charitable person, they are more likely to want to give to charity than any person on the street," said Stinton.
"So that list of people would be a good list. Maybe we can share the data, maybe we can sell the data.
"In Smile Train's case, it was less than 1 per cent of revenue."
Stinton said the practice was so widespread it would have been difficult to find a charity that did not share data.
The British Red Cross told programme makers that it had never sold donors' data it no longer shared such information with other charities.
The Information Commissioner's Office says charities can share donors' data with other specified types of charity if individuals given their permission for this to take place.