The Christian donor organisation Stewardship has estimated that £11.7m of the donations it receives each year might be affected by a new cap on tax relief on charitable donations.
The measure, announced by Chancellor George Osborne in last week’s Budget, will mean that the tax relief an individual can claim in any one year will be limited to a quarter of their income or £50,000, whichever is higher, from April 2013.
Kevin Russell, technical director of Stewardship, said a survey of his organisation’s database revealed that more than a fifth of Stewardship’s £55m income came from donations of more than £50,000.
"We don’t know how many of these donations will be affected because we don’t know the income of the donors," he said. "We’re trying to establish that."
Russell said that a significant number of Stewardship’s donors were "sacrificial givers" and contributed the majority of their income to charity.
"I’ve spoken to several donors who do this and they’re considering radically cutting their giving," he said. "One said: ‘I’ll just leave it in my company and take it out when better times come along.’
"Another guy gives £900,000 a year, out of an income of about £1m. He said he’d cut that down to £200,000 and wait to give the rest until they get rid of the rule."
Russell said the policy was a "direct attack on charitable giving" and an attempt to cast giving to charity as tax avoidance.
"It’s one thing to introduce a particularly crass policy," he said, "but it’s an even worse one to introduce a crass policy that runs counter to all the other policies you’ve introduced."